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Full text of "The geology of the Aroha subdivision, Hauraki, Auckland"

-^.4 



NEW ZEALAND 



1913. 



■ '^°' ' A.^ Karangahake Mtn. 
noo' ' ^"^ (Contour paralld with and 14 chains Sth.of Section Line) 




Vertical Section along Line A- B (Plan N- 7) 



Natural Scale 

^ . . . . 



FEET 100 50 



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8 




Tf aca^inpa/if SuljUli 




MAP OP 

SHOWING CLAIMS, REEFS, AND PRINCIPAL WORKINGS 

Scale 



1. 



Compiled frtm plani In Ihe posstssion of 
the Talisman, Crown, and Dominion 



DrtL-m\.Try Q EM'izrrw ^/rz 




By Authority: John Mackay, Governmeat Printer. 



To maimpajiy SuUdin Ni' 1C. ArvhcSuhdwi.iion .Houuraki DvvUior, . Axicila/uf Lo'ir/ District 



GEOLOGICAL MAP OF 
SUR¥E¥ DISTEICTS 

Scale of Chains — 



Reference 

Rnojda eJuMVTi Uvus 

Trades 

TrigonometrUal StaUonB — „ ~- „- C@/af 

Edges of Bush ' 

ItaiUvayL 

Waterfblla and Deana _ „ _*'"^ 




To accjompajij SnUehii jVi' W. Aroha Sitbdhv i^ioji . HcLurafu Dt-visiorv. AitxJiJnrtd Land DutrirTl 




JO,,'/ T A. 'N E ptW A. I W 

GEOLOGICAL MAP OF 



Reference 

Roads s)u}wn, thiLa ^^■^^^ea 

TVcuAs ji ,, _ ,„.«■•■■..■ 

Tri^orwmetrical Stationa „ » - C ©iB^i' 

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RaiVivap/a „ „_ „mn 

Waterfhtlo and Dams „ „ _ „,J'-x^ 



IT \^K \F\ 




- Scale of Chains - 



P.C.MORGAN, 



T l-l 1-^ l-H 1-^ 



63360 

— Reference to Geolo g ical Coloure and Si gna - 



Cenifiilid {torn data ablmiud from tin Lands and Sunn DtbarUnetit. /torn 
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Rec«nt 1 1 


Rh^it 


S«-i«6. 


Younger^ 

Older — 


Fm^rMTTfnl 1 1 




Tauranqa BaJ6 1 1 


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Coal outcrops /^ 

Outcrops with observed strihe and dip X 



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rg, 



MAP OF 

TIE MEOMA MS1"2M(S All 

(Based, on ait old map i/i Oie Wardifri:^ omce . Te AtoIiu.) 

SHOWING CLAIMS, REEFS. 8(C. 

Scale 



Unj^n iy GSSams. ^/iX 



N EW ZEALAND 



^epavtxnent 




^ of "aJtittes. 






GBOLOGHCAL SURVEY BRANCH 

(P. G. MORGAN. Director.) fil^^ 



BULLETIN No. 16 (NEW SERIES). 



THE GEOLOGY 



OF THE 

AROHA SUBDIVISION, 

HAURAKI, AUCKLAND. 



J. HENDERSON, ASSISTED by J. A. BARTRUM. 



ISSUED UNDER THE AUTHORITY OP THE HON. WILLIAM ERASER, MINISTER OF MINES 




WRLLIN(rrON. 

BY AUTHORITY: JOHN MACKAY, GOVKRNMENT PRINTER 

1913. 



LETTEE OF TRANSMITTAL. 



Geological Survey Office, 

Wellington, 25th August, 1913. 

Sir, — 

I have the honour to submit herewith Bulletin No. 16 (New 
Series) of the Geological Survey Branch of the Mines Department. 

The field-work in connection with this Bulletin was done by Dr. J. 
Henderson and Mr. J. A. Bartrum. The report itself has been written 
by Dr. Henderson, with the assistance of Mr. Bartrum in tabulating data, 
&c., and deals with the general and economic geology of the Aroha 
Subdivision, which includes the Karangahake and Te Aroha Goldfields, 
and has an area of 662 square miles. It contains 127 pages of letter- 
press, and is illustrated by a number of maps, diagrams, and plates. 

The whole of the mining-areas — in all 1,880 square miles — within 
the Hauraki Subdivision have now been geologically surveyed in detail. 
The present Bulletin is the fourth — the others being Nos. 4, 10, and 15 — 
dealing with the Hauraki mining districts. The final area, a small block 
of country near Te Puke, is being described in this year's annual report 
by Mr. J. A. Bartrum. 

I have the honour to be. 
Sir, 
Your obedient servant, 

P. G. MORGAN, 

Dii'ector, New Zealand Geological Survey. 

Hon. W. Fraser, 

Minister of Mines, Wellington. 



CONTENTS. 



Lettkk 01' Transmittal 



iii 



Chapter I. — ^Gbneral Informatiok. 



Introduction 

Field-work and Acknowledgments . . 

Climate 

Flora 



Page 




1 


Fauna 


1 


Previous Observers 


2 


Literature 


3 





Page 
3 



Population ' . . 
Means of Communication 
Industries 

Introduction . . 
Milling Industry 

Historical Account . 
Karangahake 
Te Aroha 
Owharoa 
Waitakohe 



Chapter II. 
10 
10 
12 
12 
12 
12 
12 
13 
16 
16 



-CXTLTURE. 




Industries — continued. 




Mining Industry — continued. 




Mining and Treatment of Ores 


16 


General Labour Conditions 


17 


Financial Conditions 


17 


AgriciUtural Industries 


.. 18 


Timber Industry 


18 


Fishing Industry 


1!) 



Chapter III. — Physiography. 



General Features 
Mountains 
Plains . . 
Rivers 

Rivers of the Hauraki Plain 

The Ohinemuri River . . 

Other Branches of the Waihou 

Streams draining to the Bay of Plenty 
Waterfalls 



20 
20 
20 
21 
21 
21 
23 
23 
23 



Chapter IV.- 
Te Aroha Group of Mineral Springs . . 30 

Okauia Group of Mineral Springs . . . . 36 

Waitoa Group of Mineral Springs . . 37 



Introduction . . . . . . . . 46 

North-west Faults . . . . . . 47 

North-east Faults . . . . . . 48 

Other Faults . . . . . . . . 49 

The Thames Fault-complex . . . . 49 

The Miranda Fault-complex . . . . 51 

The Bay of Plenty Fault-complex . . 51 



Chapter VI .- 



Preliminary Statement . . 
Views of Other Writers . . 
The Trias-Jura Series 
The Andesite Series 

Distribution . . 

Succession 

Petrology 

Age and Correlation 
The Dacite Series 

Distribution . . 

Succession 

Petrology 

Age and Correlation 
The Rhyolite Series 

Distribution . . 

Succession 

Petrology of the Older Rhyolites 

Petrology of the Younger Rhyolites 

Age and Correlation 



55 
57 
57 
58 
58 
59 
59 
63 
63 
63 
64 
65 
67 
68 
68 
68 
69 
70 





Swamps, &c. 


24 


The Coast-line . . 


.. 24 


Tauranga Harbour 


.. 25 


Islands 


.. 25 


Springs 


26 


Influence of Man 


.. 26 


Deforestation 


.. 26 


Drainage of Swamps . . 


.. 28 


Conclusion 


.. 28 


-Mineral Springs. 






Katikati Group of Mineral Springs 


. . :i9 




Origin of Mineral Springs 


. . 39 




Conclusion 


.. 49 


v.— Faults. 






Age of Faults . . 


.. 51 




Structure of Aroha Subdivision 


.. 52 




Hangawera Earth-block 


.. 52 




Rift Valley . . 


.. 52 




Cape Colville Earth-blook 


.. 53 




Coastal Plain 


54 


General Geology. 






The Dyke Series 


.. 73 




Distribution . . 


73 




Petrology 


74 




Age and Oirreiation 


75 




The Tauranga Series 


75 




Distribution . . 


75 




Succession 


.. 76 




Age and Correlation 


77 




Recent Deposits 


77 




The Hauraki Petrographical Piovii 


ee . . 78 




Cause of Volcanic Eruptions 


80 




Extent and Nature of the Andesite 


Aceuinu- 




lations 


81 




Period of Propylitization. . 


81 




Correlation of the Rhyolites a 


ul Po!»t- 




Rhyolitic Dykes 


82 




Geological History 


82 



VI 



Chapter VII. — Economic Geology. 



Karaiigahake Miniug-avea 

Physiography . . 

Faulting 

Lode Fissures 

PropyUtization 

Weathering . . 
Te Aroha Mining-area 

Physiography and Faulting 

Lode Fissures 
Owharoa Mining-area 
Waitakohc Mining-area . . 
Lode Minerals . . 
Facts observed in connection with 
deposits 

PropyUtization 

Persistence of Lodes in Depth 

Gangue 

Distribution of Metallic Contents 





84 




84 




84 




85 


. 


86 




87 




88 




88 




88 




89 




89 




89 


the Ore- 






92 




92 




93 




94 


of Lodes 


94 



Facts observed, &c. — continued. 

Influence of Faults, &c. 

Influence of Present Topography 

Nature of Country 

Nature of Mine-waters 

Physico-chemical Data 

Summary 
Genesis of the Ore 

Introduction . . 

Ascension Theory 

Secondary Enrichment Theory 

Lateral Secretion Theory 

Conclusion 
Future Prospects 



Te Aroha 
Waitakohe 



Pag* 

97 
97 
98 
99 
100 
101 
102 
102 
102 
103 
104 
107 
108 
108 
109 
109 



Chapter VIII. — Mining Claims. 



Talisman Consolidated . . 




. 110 


Area and Production . . 




. 110 


Maria Lode . . 




. Ill 


Other Lodes . . 




. Ill 


Faults 




. 112 


Underground Workings 




. 112 


Drainage 




. 112 


Ore-treatment 




. 113 


Power 




. 113 


Costs 




. 113 


Crown Mines 




. 113 


Area and Production . . 




. 113 


Welcome Lode 




. 114 


Other Lodes . . 




. 114 


Faults 




. 115 


Chapter IX. — Summary 


OF THE 


EcoNO 



Gold-silver Mining . . . . 119 

Metalliferous Deposits other than Gold-silver 
Lodes .. .. .. ..120 

Stone for Commercial Purposes . . . . 120 

Clays .. .. .. .. ..120 



Crown Mines — continued. 

Underground Workings .. .. 116 

Drainage . . . . . . . . 115 

Ore- treatment . . . . . . 116 

Power ..116 

Costs . . . . . . . . 116 

Dominion Gold- mining Company .. .. 116 

Te Aroha Claims . . . . . . 116 

Hardy's Mines . . . . ..116 

Waitawheta Gold-prospecting Company .. 117 

Bendigo Gold-mining Company . . . . 117 

Seddon Gold-mining Company .. .. 118 

TuiMine " .. ..118 

Eliza Mine .. .. .. ..118 



Possibilities of the Aroha Subdivision. 

Lignite . . . . . . . . 121 

Soils .. .. .. .. ..121 

Timber .. .. .. ..122 

Kauri-gum . . . . . . . . 122 



Index 



123 



Temperature 

Rainfall 

Mineral Production of Karangahake Mining- 
area 

Mineral Production of Te Aroha Mining-area 

Tidal Range of Tauranga and neighbouring 
Ports 

Radio-activity of To Aroha Springs 

Composition of Waters from Te Aroha Hot 
Springs . . . . . . 32, 



Tables. 

2 
2 



13 
15 

26 
30 

33 



Composition of Waters from Te Aroha Cold 
Springs . . . . . . 34, 35 

Composition, in Ions, of Te Aroha Hot Springs 42 

Composition; in Ions, of Te Aroha Cold Springs 43 

Gteologioal Formations . . . . . . 57 

Rock Analyses of Hauraki Province . . 79 

Ore Analyses from Karangahake . . . . 95 

Assays of Karangahake Rocks . . . . 106 



Vll 



PLATES 



I. Part of Cape Colville Range, from Kafcikati. {Frontispiece.) Facing page 



II. Karangahake and the Ohinemuri River, looking North . . . . . . . . . . 21 

III. Wairere FaUs .... . . . . . . . . . . . . . . 23 

IV. Maunganui Mount, from Tauranga Spit . . . . . . . . . . 1 25 

Monmouth Redoubt, Tauranga . . . . . . . . . . . . ) 

V. Okauia Step-faults, looking South from Wairere Stream . . . . . . . . . . 36 

VI. Rock Plate at Head of Wahine Creek . . . . . . . . . . . . 1 48 

Knobs of Rock at Head of the Waipupu, showing Waipupu Pond in Foreground . . ) 

VII. Hypersthene Quartz Andesite, showing Alteration of Groundmass due to Propylitization . . 61 

VIII. Wilsonite. Reflected Light. 10 diameters . . . . . . . . . . I 70 

Wilsonite. Transmitted Light. 25 diameters . . . . . . . . . . | 

IX. Te Aroha Domain. Bald Spur in Background . . . . . . . . . . '-88 

Buck Reef, Waiorongomai . . . . . . . . . . . . . . ) 

X. Karangahake Mountain, showing Talisman Power-house and Mill in Foreground . . | j j ,^ 

Talisman Power-house . . . . . . . . . . . . . . J 



DIAGRAMS, ETC. 



Facing paije 
..3 
..31 
..79 
.. ..85 

..89 
Page 

Plan showing Migration of Meanders of Waihou River, Wairere Survey District '. . . . 29 

Diagramatic Section across the Aroha Subdivision . . . . . . . . . . . . 54 



Map showing Distribution of Kauri . . 

Map of Te Aroha Domain . . 

Diagram showing Variation of Rocks of Hauraki Province 

Diagram of Lode Fissures, Karangahake 

Diagram of Lode Fissures, Te Aroha 



MAPS AND SECTIONS. 

Facing page 

No. 1 . Map of New Zealand showing Divisions . . . . . . . . . . viii 

No. 2. Map of Hauraki Division showing Survey Districts and Area geologically surveyed viii 

No. 3. Geological Map of Waitoa Survey District . . . . . . . . . . In portfolio. 

No. 4. Geological Map of Aroha, Katikati North, Katikati, and Matakana Survey Districts 

No. 5. Geological Map of Wairere and Aongatete Survey Districts . . . . . . „ 

No. 6. Geological Map of Tauranga Survey Districts . . . . . . . . . „ 

No. 7. Map of Karangahake Mining-area . . , . . . . . . . , . ,, 

No. 8. Longitudinal Sections of Crown and Talisman Mines .. .. .. .. „ 

No. 9. Cross Section, Karangahake Mining-area . . . . . . . . . . „ 

No. 10. Map of Te Aroha Mining-area . . . . . . . . . . . . ,, 




B000.*.09.3I8. 



By Authority : John Uackay, Gcvtmmcnt Printer. 



COLVILLE, 



MOEHAU 



FfTZ^OY rrRYPHENA 

J:5 



<C>i 




IROMANDEL 



lASTINGS 




(?.ifV. 



MERCURY 




fawato 




P.G. MORGAN. 
OIRCCTOfl. 



MAP OF 

HAURAKI DIVISION 

SHOWING SURVEY DISTRICTS 

AtoJvcu Stihdiviston/ ( B\dle tirbl^'^ 16 J 
coloured' thus f I 

Svd>diiytstons dealt with trv previous huUetins 
coloured thus I I 



ENGLISH MILES 
10 



20 



SOUTH PACIFIC 



WAIHI NORTH 




OCEAN 



^>' 



lOIANEWAINUKU 



TeRikel 
MAKETl!; 



TAPAPA EASl 



OTUTARA 




AWApkATyA' 



E JTirtiu 

ROXTORUA 



DIVISION 



By Authority ■ John ftjaokay, Oovtrnment Printer 



BULLETIN No. 16 (NEW SERIES). 



THE GEOLOGY 



OP THE 



AEOHA SUBDIVISION, 



HAURAKI, AUCKLAND. 



CHAPTEE I. 



GENERAL INFORMATION. 





Page 




Introduction 


1 


Fauna 


Field-work and Acknowledgments 


1 


Previous Observers 


Climate 


.. 2 


Literature . . 


Flora 


.. 3 





Page 
3 
4 
5 



Introduction. 

The area described in the present bulletin includes the survey districts of Waitoa, 
Aroha, Katikati North, Katikati, Matakana, Wairere, Aongatete, and Tauranga. It 
may be conveniently termed the Aroha Subdivision of the Hauraki Division. The 
Thames and Waihi subdivisions, described in Bulletins 10 and 15 respectively, adjoin 
it on the north. The subdivision contains in all about 662 square miles, and of this 
area about 250 square miles is hilly, in parts moimtainous, and in the main densely 
forested. The remainder is mostly flat, in part swampy, grassed or covered with fern 
and low scrub. 

The mineral wealth of the subdivision is considerable, and at Karangahake the 
mining industry is in a very flourishing state. 

The Kauri Timber Company and the Waihi Rawmilling Company are actively 
cutting out the remnants of the kauri bush at the heads of the Waitawheta and Wairoa 
streams. 

The principal wealth of the district, however, lies in its wide pasture lands. 

Field-work and Acknowledgments. 

The field-work upon which this bulletin is based extended over a period of ten 
months — from August, 1911, to May, 1912, inclusive. Throughout this period the writer 
was assisted in the field-work by Mr. J. A. Bartrum, M.Sc. In the autumn of 1911 
1 — Aroha. 



Mr. K. M. G-raham, formerly of the Geological Survey, had completed a topographical 
survey of the Waitawheta basin and some of the streams near Te Aroha. All 
analyses quoted in this bulletin, unless it be otherwise expressly stated, are due to 
Dr. J. S. Maclaurin, Dominion Analyst, and his staff. 

The thanks of the Geological Survey are due to the managers of the various 
mines now in active operation, and more especially to Messrs. H. Stansfield, of the 
Talisman, and J. McCombie, of the Crown Mines, without whose assistance the preparation 
of the map of the Karangahake Mining-area would have been impossible. 



Climate. 

The climate of the Aroha Subdivision is, on the whole, warm and moist. Owing 
to the proximity of the sea, extremes are unknown even on the western sid« of the 
Cape Colville Range. The mean monthly temperature at Te Aroha* is as follows ; — 



Jan. 


Feb. 


March. 


April. 


May. 


June. 


July. Aug. Sept. 


Oct. 


Nov. 


Deo. 


Mean for 
the Year. 


67-7° 


66-5° 


644° 


57-9° 


54-1° 


51-8° 


49-2° 50-6° 53-4° 


57-1° 


63-0° 


65-4° 


58-4° F. 



For Tauranga the mean temperature is slightly greater, but no exact figures are 
available. The winters are short ; and while freezing temperatures are usually experienced 
in each of the winter months, a temperature of 25° Fahr. is almost unknown, and 
frosts are of short duration even on the Piako Swamp lands. The summers are long ; 
and, though the extreme of summer temperature is not excessive, the high atmosphejic 
humidity makes the heat somewhat oppressive at times. The highest temperatures 
are experienced on the Hauraki Plain, but the thermometer rarely registers 80° Fahr. 
in the shade, and never 90°. 

From casual observation, it is hard to say what the direction of the prevailing 
wind is. The writer is inclined to think that the south-west is the commonest quarter 
from which the wind comes, but north-east winds are also very frequent. Under the 
abrupt western wall of the Cape Colville Range from Te Aroha to Okauia, the wind 
crossing from the range is apt to attain cyclonic violence, and much damage to 
property has been occasioned at times. 

Any northerly wind may bring rain, while showery weather is to be expected 
from the south-west. The following table* shows the rainfall at various points within 
or near the subdivision : — 

Mean Raineall, in Inches. 



Station. 


Jan. 


Feb. March. 


April. 


May. 


June. 


July. Aug. 


Sept. 


Oct. 


iNumber 
Nov. Dec. Total. 1 of 
i j 1 Years. 


Waihi . . 


5-47 


4-61 


9-21 


5-93 7-98 


6-89 


9-84 


8-42 


7-61 


7-10 


4-47 


5-53 


8306 i 13 


Athenree 


4-50 


4-98 


4-79 


4-72 


6-48 


502 


7-75 


6-30 


5-38 


4-80 


4-08 


3-90 


62-70 


18 


Tauranga 


4-95 


3-52 


3-66 


4-54 


5-80 


4-17 


5-55 


3 47 


419 


4-85 


2-63 


3-39 


50-72 


10 


Te Aroha 


3-37 


3-69 


4-25 


4-03 


6-28 


5-22 


6-59 


5-87 


5-43 


3-92 


3-72 


3-38 


65-75 


13 



It will be noted that the precipitation is very evenly distributed throughout the 
year, and that the eastern side of the range has a somewhat heavier fall than the 
western. Rainfall on the mountains is much heavier and more frequent than on the 



* Supplied by the Dominion Meteorologist. 




MAP SHOWING 

Distribution of Kauri intheAroha Subdivision 



1 /i 

- 



Scale of Miles 

12 3 4 

I I I I 



Existing groves shown thus '^^ ][ Sporadic Trees shown thus* S 
7 ,; CCv^ Jl Gu 



Groves cut out 



jm 



Geo. Bull. No. 16.~\ 



■X X 



{To face p. 3. 



lowlands, but there are no stations at which records of the precipitation on the range 
are kept. The heavy rainfall at Waihi* is, however, sufficiently suggestive. Snow 
rarely falls, and then only during the severest winter storms, and upon the highest 
crests. 

Flora. 

The description of the flora of the Coromandel Subdivision in Bulletin No. 4 
applies to the flora of this subdivision. As, however, the southern limit of the 
mangrove and the kauri is within the district, a few remarks on the distribution of 
these may not be out of place. 

That the subtropical mangrove should not venture farther south than the warm 
mud-flats of the sheltered Tauranga Harbour is not a matter for astonishment. Even 
there, however, it does not thrive. 

The distribution of the kauri presents a much more difficult problem. Within 
recent times kauri groves, as distinct from sporadic trees, have not occurred farther 
south than the Whakamarama Plateau. Even here, at the southern limit of the 
kauri's distribution, the tree still prefers the precipitous sides of the ravines and the 
relatively bleak crests and plateaux. Within the subdivision it is only in the valley 
of the upper Waitawheta that the trees descend in any number to the bottoms of the 
valleys ; and there the distribution is capricious and difficult to explain, for 
localities which provide an apparently suitable habitat, similar in every way to other 
immediately contiguous places densely covered with kauri, are left without a single 
tree. Such a locality is furnished by the Waipapa. There no kauris grow, although 
the main Waitawheta both above and below its junction has kauri forest on both 
banks. In regard to this forest, the fewness of decrepit trees and the comparative 
absence of gum are locally thought to indicate the youth of the forest. 

The accompanying map shows what the distribution of the kauri was within, say, 
the last fifty years. A few trees are growing on Te Aroha Mountain ; a small grove 
occurs in the upper Waiorongomai ; a few trees were observed in the Wairakau ; and 
a grove occurs in the rough country near the head of the Puketutu. A grove of 
perhaps two hundred trees was observed near the head of the north branch of the 
Waiteariki, and this, as far as the writer could learn, is the most southerly grove 
on the eastern side of the North Island. On the Bay of Plenty side of the range 
a few trees are to be found in the basins of the Te Rere-atu-kahia and Waitakohe ; 
and the writer is informed that at one time kauris grew in the Kauritutahi Stream 
— -that is, the stream of the first kauri — but these were nol; observed. 

The kauri was formerly more widely distributed in the district. Kauri Point 
takes its name from the fact that kauri once grew there. Gum has been dug on 
Matakana Island, in the basin of the Whatakao, on Mount Hikurangi, in the Waiau 
Gorge, and on the hills between the Waihi Plain and the sea. From all these localities 
forest growth of any description has vanished. Probably the fires started by the 
Maoris when first they came to the district were responsible for this destruction. 
Submerged kauri logs are found in the Piako Swamp, and gum was at one time 
scattered over the Hauraki Plain. The burning of the vegetation following on drainage 
operations has destroyed these evidences of the former extension of the kauii. 

Fauna. 
The fauna of the subdivision is similar to that described in Bulletin No. 4 on the 
Coromandel Subdivision. Similar conditions of climate and vegetation prevail. 



* See also Devereux, H. B. : " The Remarkable Rainfall and Meteorology of Waihi." (Trans., vol. xiii. 
1909, pp. 408-11.) 

1* — Aroha. 



The Chinese pheasant* {Phasianus torquatus) was liberated first in New Zealand 
in 1851 at Waitakerei, near Auckland, and by 1869 was abundant on the Hauraki 
Plain. Some years before this latter date they were also liberated at Tauranga. 
They are now fairly abundant throughout the subdivision. 

The Calif ornian quail* (Callipepla californica) was turned out at Papakura in 
1862, and is now very abundant. It is greatly disliked by farmers, who charge it 
with all manner of delinquencies. 

Hares are common over the whole district, but the rabbit does not seem to have 
yet reached the eastern side of the range, although abundant near Okauia. 

Concerning the native fauna, little need be added to the account given in Btdletin 
No. 4. The tuatara, long extinct upon the mainland of New Zealand, still maintains 
itself upon the rhyolitic islet of Te Karewa, seven miles north-north-west of Maunganui 
Mount. Hochstetterf states that it was reported to exist upon Motu Otau, but in 
this he was probably misinformed. 

The dangerous katipo is probably abundant on the beaches and littoral swamps of 
the subdivision, although the writer observed none. 

The New Zealand frog {Liopelma hochstetteri), although searched for in likely places, 
was not found. The kiwi, pukeko, weka, and other native birds were observed, but 
are relatively very rare. The far-wandering godwit haunt the mud-flats and mangrove 
swamps of Tauranga Harbour at certain seasons of the year. 

Previous Observers. 

From the list of literature given below it will be gathered that many references 
have been made to the geology of the district. Nearly all of these references are of a 
most cursory nature, and relate to the immediate neighbourhood of the mining centres 
of Waihi, Karangahake, and Te Aroha. 

Dieilenbach, as early as 1841, crossed from Tauranga to the Hauraki Plain, and 
thence down the Piako River. He noted the lignite beds near Tauranga, that the rocks 
forming the range were of volcanic origin, and that the Hauraki Plain was largely 
formed of pumice sands. 

Hochstetter, in 1859, followed almost the same route as Dieffenbach. He noted 
that the Cape Colville Range reaches the Whanga Plateau, an extension of the Paterere 
Plateau of the Rotorua district. 

Cox, in 1882, examined the Te Aroha and Karangahake districts. He considered 
that the range between Te Aroha and Karangahake was built up of alternate layers of 
lava and sandstone (ash-beds). His classification of the rocks of the whole peninsula has 
been followed in the main by later writers. His report contains many valuable 
observations in connection with the lodes of the subdivision. 

Cussen, in 1893, discussed at length the former courses of the Waikato. He 
considered that at one time it flowed to the Bay of Plenty, that later it reached the 
Hauraki Gulf by the course of the present Waitoa, and that the change of its discharge 
to the Tasman Sea was of recent date. 

McKay has examined, at one time or another, almost the whole of the Hauraki 
Peninsula, and has written numerous papers and reports recording his observations 
and views. 

Park has also travelled widely over the peninsula. His views are to be found in 
numerous publications. He early called attention to the wide distribution of the acid 

* Hutton, F. W. :. Trans., vol. ii, 1869, p. 80. 

t Hochstetter, F. vonj: " New Zealand," 1867, p. 442. 



rocks of the peninsula. These he considers, in part at least, contemporaneous with the 
rhyolites of the Taupo zone. 

Lindgren, in 1905, noted that the Hauraki Plain was a down-faulted area or gniben 
valley. 

Bell and Fraser, in Bulletins Nos. 10 and 15, deal with areas contiguous with and 
similar to the area here described. Many of their more general remarks apply to the 
Aroha Subdivision. 

Literature. 

Many reports and notices have appeared dealing with the physiography, geology, 
and mining industry of the area within the Aroha Subdivision, and, so far as concerns 
the more important of such notices and reports, the following list of authors and their 
publications is believed to be fairly complete : — 
The abbreviations used are, — 

Q.J.G.S. : Quarterly Journal of the Geological Society of London. 
Trans. : Transactions of the New Zealand Institute. 
Eep. G.S. : Reports of the Geological Survey of New Zealand. 
Mines Rep. : Papers and Reports relating to Minerals and Mining (N.Z.). 
Aust. Ass. Adv. Sc. : Reports of the Australasian Association for the Advance- 
ment of Science. 
• Trans. Aust. Inst. Min. Eng. : Transactions of the Australasian Institute of 
Mining Engineers. 
Jour. Roy. Soc. N.S.W. : Journal of the Royal Society of New South Wales. 
N.Z.G.S. : New Zealand Geological Survey. 

A capital letter followed by a figure (thus, C.-3) refers to a New Zealand 
parliamentary paper. 
1843. Dieffenbach, Ernest : " Travels in New Zealand," vol. i, pp. 403 et seq. 
1859. Heaphy, C. : Proceedings of Geological Society of London, vol. xvii, 1860, p. 242. 
Shows map of North Island of New Zealand, in which the Cape Colville 
Peninsula is represented as consisting of a porphyritic rock with quartz veins, 
and of black conglomerate. 
1864. Hochstetter, F. von : " Geologic von Neu-Seeland : Beitrage zur Geologie der 
Provinzen Auckland und Nelson." " Novara " Expedition, Geologischer Theil, 
I band, I Abtheilung. 

1867. Hochstetter, F. von : " New Zealand," pp. 439 et seq. 

1868. Crawford, J. C. : " Essay on the Geology of the North Island of New Zealand " 

(written for the New Zealand Exhibition, 1865). Trans., vol. i, p. 325. 
Reference is made to occurrence of auriferous quartz in Hangawera Range. 

1870. Hector, James : " On the Geology of the Cape Colville District." Rep. G.S., 
vol. vi, 1871, pp. 99-103. 

1872. Hutton, F. W. : " On the Past Great Glacier Epoch in New Zealand." Trans, 
vol. V, p. 392. Mentions that the uprise of the Lower Waikato Valley in the 
Pleistocene period has not been more than 50 ft., and that the focus of greatest 
uplift during that period was the central portion of the North Island. 

1880. Smith, S. Percy : " On some Indications of Changes in the Level of the Coast-line 

in the Northern Part of the North Island." Trans., vol. xiii, pp. 398 et seq., 
especially p. 407. 

1881. Hector, James: Progress Report. Rep. G.S., vol. xiv, p. x, 1882. Refers to 

the southward extension to Te Aroha of the Thames Gold-niining District. 
1881. Cox, S. H. : " North Auckland District, including Thames, Coromandel, Island of 
Kawau, and Drury Coalfield." Rep. G.S., vol. xiv, 1882, p. 39. 



6 

1881. Cox, S. H. : " On certain Points connected with the Geology of the Auckland 

District." Eep. G.S., vol. xiv, 1882, pp. 96-97. Describes the Te Aroha 
Goldfield and the Piako District. 

1882. Hector, James : Progress Report. Rep. G.S., vol. xv, 1883, pp. xii-xiii. 

1882. Cox, S. H. : " Goldfields of the Cape Colville Peninsula." Rep. G.S., vol. xv, 1883, 

pp. 20-51. Contains the first systematic account of the Karangahake and Te 
Aroha districts. 

1883. Bramhall, H. : " The Mineral Resources of New Zealand." Transactions Liverpool 

Geological Association. 
1883. Cox, S. H. : " On the Occurrence of some New Minerals in New Zealand." 

Trans., vol. xvi, p. 449. Notes occurrence of tellurides at Karangahake and Te 

Aroha. 
1883. Hunter, Ashley : " Direct Evidence of a Change in the Elevation of the Waikato 

District." Trans., vol. xvi, pp. 459-60. Notes evidence of depression afforded 

by observations on pier sinking near Hamilton. 
1885. Skey, W. : Halloysite at Karangahake. Colonial Museum and Laboratory. 

19th Annual Report, p. 29. 

1885. Skey, W. : Tellurium from Karangahake. Colonial Museum and Laboratory. 

19th Annual Report, p. 37. 

1886. Larnach, W. J. M. : " Handbook of New Zealand Mines." (Preface.) Refers to 

galena and cinnabar at Tui Creek, Te Aroha. 

1886. Galvin, P. : " Handbook of New Zealand Mines," pp. 281, 316-29. Reference 

to finding of gold at Te Aroha in 1880 and to occurrence of tellurium at 
Waiorongomai. 

1887. Pond, J. A. : Extracts from paper on the minerals of Cape Colville Peninsula. 

Mines Rep., p. 56. Fresh occurrences noted are wad, hyalite, and opal from 

Karangahake. 
1887. Gordon, H. A.: "North Island Mining Generally." Mines Rep., pp. 27, 31, 121, 

123. 
1887. Hutton, F. W. : " On the Rocks of the Hauraki Goldfield." Aust. Ass. Adv. Sc, 

vol. i, pp. 245-74. 

1887. Skey, W. : " On Gold : Its Formation in oiir Reefs, and Notes of some newly 

discovered Reactions." Aust. Ass. Adv. Sc, vol. i, pp. 155-68. 

1888. Gordon, H. A. : " Mining Generally." Mines Rep., C.-5, p. 27. 

1889. Montgomery, A. : Mention of occurrence of selenium in Ohinemuri district. Mines 

Rep., C.-2, p. 20. 
1889. Gordon, H. A. : " Mining Generally— Quartz Mining." Mines Rep., C.-2, p. 39. 

1889. Hutton, F. W. : " The Eruptive Rocks of New Zealand." Jour. Roy. Soc. 

N.S.W., vol. xxiii, p. 102. 

1890. Hseusler, Rudolf : " On the Microscopic Structure of the Ohinemuri Gold." 

Trans., vol. xxiii, pp. 335-40. Refers to occurrence of gold, silver, mercury, 

cinnabar, and natural amalgam at Owharoa. 
1890. Park, James : "On the Geological Structure and Future Prospects of the Thames 

Goldfield, New Zealand." Aust. Ass. Adv. Sc, Melbourne, vol. ii, p. 429. 

Park considers the auriferous series — Lower Eocene in age — to be exposed in the 

denuded cores of anticlinal folds with a north-east trend, the overlying Upper 

Eocene beds of volcanic breccias and tuffs having been thence removed. 
1890. Gordon, H. A. : " Quartz Mining." Mines Rep., C.-3, pp. 37, 42. 
1891.. Gordon, H. A. : " Quartz Workings." Mines Rep., C.-4, pp. 34, 42. 
1892. Gordon, H. A. : Mines Rep., C.-3, p. 45. References to mines of Karangahake 

and Te Aroha. 



1892. Hector, James: "Minerals of New Zealand." Eep. G.S., vol. xxi, pp. 112-14 

(Appendix). Hessite recorded from Te Aroha — W. Skey, analyst. 
189.3. Park, James : " On the Occurrence of some Rare Minerals in New Zealand." 
Trans., vol. xxvi, p. 366. Notes occurrence of pyromorphite, anglesite, and 
cerussite at Te Aroha. 

1893. Cussen, Lawrence : " Notes on the Piako and Waikato River Basins." Trans., 

vol. xxvi, pp. 398-407. 

1893. Mines Rep., C.-3, pp. 62, 70. References to the mines of Karangahake and Te 

Aroha. 

1894. Mines Rep., C.-3, pp. 42, 47. Reference to mines at Karangahake and Te Aroha. 

1895. Mines Rep., C.-3, pp. 53, 65. Reference to mines at Karangahake and Te Aroha. 

1896. Mines Rep., C.-3, pp. 67, 72, 78. Reference to mines at Karangahake and Te 

Aroha. 
1896. Cadell, H. M. : Paper read before the Mining Institute of Scotland. (See Mines 
Rep., C.-3, p. 81.) 

1896. Campbell, Joseph : " The Goldfields of the Hauraki Peninsula, New Zealand." 

Transactions of the Federated Institute of Mining Engineers. 

1897. Wilson, George : " Quartz Mining." Mines Rep., C.-3, pp. 87, 97. 

1897. McKay, Alex. : " Report on the Geology of the Cape Colville Peninsula, Auckland." 

Mines Rep., C.-9, pp. 1-75. 
1897. McCombie, John : "A Retrospect of the Ohinemuri Goldfield." Neiv Zealand 

Mines Record, vol. i, p. 33. 
1897. McCombie, John: "Treatment of Ore in the Hauraki Goldfield." Trans. N.Z. 

Inst. Min. Eng., vol. i. Copied by New Zealand Mines Record, vol. i, p. 399. 
1897. Park, James : " The Geology and Veins of the Hauraki Goldfield." Trans. N.Z. 

Inst. Min. Eng., vol. i. Extract in New Zealand Mines Record, vol. i, p. 168. 
1897. Wilson, George : "On some Differences that distinguish the Goldfields of the 

Hauraki Mining District." Trans. N.Z. Inst. Min. Eng., vol. ii, p. 17. 
1897. Wauchope, J. A. : " The Goldfields of the Hauraki District." Transactions of 

the Federated Institute of Mining Engineers, vol. xiv, pp. 19-45. 

1897. Campbell, J. : " Volcanic Zone of the Hauraki Goldfields." Scottish Geological 

Magazine, p. 246. 

1898. Don, J. R. : " The Genesis of certain Auriferous Lodes." Trans. Amer. Inst. Min. 

Eng., vol. xxvii, pp. 564-659. 
1898. Schiff, F. : " Les Mines d'Or de la Nouvelle-Zelande." Publications du Journal, 

" Le Genie Civil," Paris. 
1898. Wilson, George : " Quartz Mining." Mines Rep., C.-3, pp. 66, 73. 
1898. McKay, Alex. : " Geological Survey of Cape Colville Peninsula. Progress Report 

for the Year 1897-98." Mines Rep., C.-9, p. 8. 

1898. New Zealand Mines Record, vol. i, pp. 81, 373. 

1899. Park, James, and Rutley, F. : " Notes on the Rhyolites of the Hauraki Goldfields." 

Q.J.G.S., vol. Iv, pp. 449-69. 
1899. Wilson, George: "Quartz Mining." Mines Rep., C.-3, p. 61. 
1899. McKay, Alex. : " Report on the Pumice-stone Deposits of the Middle Part of 

the North Island." Mines Rep., C.-9, p. 16. 

1899. McKay, Alex. : " Report on the Occurrence of Coal near Waihi. Auckland." 

Mines Rep., C.-9, p. 25. 

1900. Mines Rep., C.-3, pp. 84, 90. Reference to mines at Karangahake and To 

Aroha. 
1900. McKay, Alex. : " The Igneous Rocks of New Zealand." Neiv Zealand Mines 
Record, vol. iii, p. 177. 



8 

1900. Park, James : " Cyaniding in New Zealand." New Zealand Mines Record, vol. iii, 
p. 275. Mentions cyanide process as being first introduced in 1889 at the 
Crown Mines, Karangakake. 

1900. Rutley, F. : " Additional Notes on some Eruptive Rocks from New Zealand." 

Q.J.G.S., vol. Ivi, p. 493. 

1901. Mines Rep., C.-3, pp. 52, 56. Reference to mines at Karangahake and Te Aroha. 

1901. Allen, F. B. : " Tellurium in tlie Ores of the Hauraki Goldfields." New Zealand 

Mines Record, vol. iv, p. 469. Reference to nickel and cobalt at Karangahake. 

1902. Mines Rep., C.-3, pp. 41, 42, 86, 88. Reference to m,ines at Karangahake and 

Te Aroha. 

1902. Morgan, P. G. : " Geology, Quartz Reefs, and Minerals of Waihi." Trans. Aust. 

Inst. Min. Eng., vol. viii, p. 166. 

1903. Mines Rep., C.-3, pp. 23, 88-92, 145. Reference to mines at Karangahake and 

Te Aroha. 

1904. Morgan, Percy G. : " Water in the Hauraki Goldfield, New Zealand." Engineering 

and Mining Journal, New York, vol. Ixxviii, No. 11, 15th September, p. 429. 
Considers much of mine-water to have deep-seated origin, and remarks that 
the largest quartz reef in the goldfield is within two miles of the Te Aroha hot 
springs. 

1904. Mines Rep., C.-3, pp. 44, 45, 99, 101. Reference to mines at Karangahake and 

Te Aroha. 

1905. Mines Rep., C,-3, pp. 4, 5, 35, 36, 84, 85. Reference to mines at Karangahake 

and Te Aroha. 

1905. McKay, Alex., and Sollas, W. J. : " Rocks of the Cape Colville Peninsula," vols, i 
and ii, 1905-6. 

1905. Lindgren, Waldemar : " The Hauraki Goldfields, New Zealand." Engineering and 
Mining Journal, New York, 2nd Feb. See also New Zealand Mines Record, 
vol. viii, p. 370. Makes first mention of Hauraki grdben ; considers faulting 
later than formation of reefs. Present Ohinemuri River results from capture 
of a former eastward-fiowing stream. 

1905. Morgan, Percy G. : Discussion of Lindgren's article " The Hauraki Goldfields, New 
Zealand." Engineering and Mining Journal, New York, vol. Ixxix, No. 18, 
4th May, p. 861. See also New Zealand Mines Record, vol. viii, p. 465. 

1905. Allen, F. B. : Reports nickel and cobalt from concentrates of Woodstock Mine, 
Karangahake. New Zealand Mines Record, vol. viii, p. 148. 

1905. Levat, David : " L'Industrie Aurifere." p. 834. Vve. Ed., Ch. Dunod, Editeur, Paris. 

1905. Marshall, P. : " The Geography of New Zealand." Publishers, Whitcombe and 

Tombs (Limited), Wellington, New Zealand. States that Cape Colville Range 
is a remnant of a range similar to that from Pirongia to Wairoa. 

1906. Mines Rep., C.-3, pp. 4, 38-40, 92, 93. Reference to mines at Karangahake and 

Te Aroha. 
1906. Park, James: "A Text-book of Mining Geology," pp. 113-16, 136. Publisher, 

McMillan and Co. 
1906. Loughnan, R. A. : " The First Gold Discoveries in New Zealand." New Zealand 

Mines Record, vols, ix and x. Also reprinted separately. 
1906. Gordon, H. A. : " The Rise and Progress of the Gold-mining Industry." " New 

Zealand Mining Handbook," p. 7. 

1906. Bell,. J. M. : " The Salient Features of the Economic Geology of New Zealand." 

Economic Geology, vol. i, No. 8, pp. 735-50. 

1907. Mines Rep., C.-3, pp. 12-14, 49. Reference to mines at Karangahake and Te 

Aroha. 



.9 . 

1907. Goldfields and Mines Committee, I. -4a. On petitions relating to the silting-up 
of the Ohinenauri and Waihou Rivers. 

1907. Fraser, C, and Adams, J. H. : " The Geology of the Coromandel Subdivision, 

Hauraki, Auckland." Bulletin No. 4 (New Series), N.Z.G.S. 

1908. Bell, J. M., and Fraser, Colin : " The Great Waihi Mine." Canadian Mining 

Journal, vol. xxix, Nos. 16 and 17. 
1908. Mines Rep., C.-3, pp. 5, 15-17, 45. Reference to mines at Karangahake and Te 
Aroha. 

1908. MacLaren, J. M. : " Gold : Its Geological Occurrence and Geographical Distribu- 

tion." Publishers, Mining Journal, London. 

1909. Park, James : " Notes on the Geology of the Hauraki Goldfields." Neiv Zealatid 

Mines Record, vol. xii, p. 262. Considers country of Karangahake reefs to be 

of higher horizon than that of Thames and Coromandel reefs. Refers also to 

an " ancient Waitawheta volcano." 
1909. Finlayson, A. M. : " Problems in the Geology of the Hauraki Goldfields, New 

Zealand." Economic Geology, vol. iv. No. 7, pp. 632-45. 
1909. Mines Rep., C.-3, pp. 6, 23-25, 42. Reference to mines at Karangahake and Te 

Aroha. 
1909. Park, James : " History of Mining in New Zealand." Mining Journal, London, 

August. 

1909. Bell, J. M. : " Economic Geology of New Zealand." Trans. Aust. Inst. Min. Eng., 

vol. xiii. 

1910. Finlayson, A. M. : " The Ore-deposits of Waihi, New Zealand." Mining 

Magazine, London, April, pp. 281-86. 
1910. Mines Rep., C.-3, pp. 7, 16-18, 40-41. Reference to mines at Karangahake and 

Te Aroha. 
1910. Fraser, C. : " The Geology of the Thames Subdivision, Hauraki, Auckland." 

Bulletin No. 10 (New Series), N.Z.G.S. 
1910. Morgan, P. G. : " The Igneous Rocks of the Waihi Goldfield." Trans., vol. xliii, 

pp. 258-75. 
1910. Park, James : " Geology of New Zealand." 
1910. C.-8. Report on drainage operations in the Hauraki Plains. 

1910. C.-14. Report of Royal Commission on the silting-up of the Waihou and Ohine- 

muri rivers. 

1911. Mines Rep., C.-3, pp. 6-7, 19-21, 40. Reference to mines at Karangahake and Te 

Aroha. 
1911. Bell, J. M. : "The Waihi Goldfield, New Zealand." Trans. Aust. Inst. Min. Eng., 

vol. XV, pp. 548-82. 
1911. Wohlmann, A. S. : " The Mineral Waters and Health Resorts of New Zealand." 

4tli edition. 
1911. Bell, J. M. : " The Hauraki Goldfields, New Zealand." Trans. Aust. Inst. Min. 

Eng., vol. xvi, 1912, pp. 1-24. 

1911. Jarman, A. : " Mining and Ore-treatment at the Talisman Mine, Karangahake." 

Trans. Aust. Inst. Min. Eng., vol. xvi, 1912, pp. 339 et seq. 

1912. Mines Rep., C.-2, pp. 21-22, 35-38. Reference to mines at Karangahake and Te 

Aroha. 
1912. Bell, J. M., and Fraser, C. : " The Geology of the Waihi-Tairua Subdivision, 
Hauraki." Bulletin No. 15 (New Series), N.Z.G.S. 



10 



CHAPTEK II. 



CULTUEE. 



Population . . 
Means of Communication 
Industries . . 
Introduction 
Mining Industry 
Historical Account 
Karangahake . . 
Te Aroha 
Owharoa 
Waitakohe 





Page 




. 10 




. 10 




. 12 




. 12 




. 12 




. 12 




. 12 




. 13 




. 16 




. 16 



Industries — continued. 

Mining Industry — continued. 
Mining and Treatment of Ores 
General Labour Conditions 
Financial Conditions 

Agricultural Industries 

Timber Industry . . 

Pishing Industry . . 



Page 



16 
17 
17 
18 
18 
19 



Population. 

The Aroha Subdivision includes parts of three counties — Ohinemuri, Piako, and Tauranga — 
and since the official information concerning population has been compiled under counties, 
and not under survey districts, only an approximate estimate of the population of the 
subdivision can be given. 

The only port of the district — Tauranga, with 1,346 inhabitants (by the census of 
1911) — serves a large agricultural district. With the development of the arable and 
pastoral land of this district, and the extension of the railway at present under con- 
struction, Tauranga should before long be an important commercial centre. Te Aroha 
(1,298 inhabitants) came into existence as a mining town, and but for the existence of a 
group of ' hot springs at the base of the mountain overshadowing the town, would now 
be merely a small agricultural village. The flourishing mining township of Karangahake 
is on the northern boundary of the subdivision; the population of the [part within the 
district may be six hundred. The rural population is distributed along the west and 
south-west shore of Tauranga Harbour and along the western base of the Cape Colville 
Range. In both localities there are large areas of land at present unoccupied. The total 
population of European descent is about six thousand, of which about half may be 
described as rural. 

The total Maori population is estimated at between eight hundred and a thousand. 
The principal settlements are on Matakana Island (western portion), Katikati Heads, a 
scattered population around the southern end of Tauranga Harbour, and north of 
Te Aroha at Tui Pa, Mangaiti, Waitoki, and Tirohia. The largest population is around 
Tauranga Harbour. According to Native tradition, the country around this inlet was 
early occupied by the Maori colonists. Dieffenbach,* in 1841, estimated the Native 
population of the Tauranga district at three thousand. In 1859 the population 
had been reduced by internal wars and disease to between eight hundred and a 
thousand, t 

Means op Communication. 

The inhabitants of the Aroha Subdivision have ready means of communication with 
the rest of New Zealand. The townships of Te Aroha, Karangahake, and Waihi 
are in daily touch with Auckland by rail. Tauranga is connected with Auckland by 
steamer service twice a week, with Waihi by a tri-weekly and with Eotorua by a 
daily coach-service. 



* DiefEenbach, E. : " Travels in New Zealand," 1843, vol. i, p. 407. 
t Hochstetter, F. von : " New Zealand," 1867, p. 442. 



11 

Two meridionally disposed belts of country, passable with difficulty, traverse the 
subdivision.* These are the swampy Hauraki Plain and the Cape Colville Range. These 
barriers determine the disposition of the railway and the main roads. Thus the 
railway crosses the Hauraki Plain at its southern end, and then follows the relatively 
firm strip between the swamp and the mountains. Again, the Morrinsville-Miranda 
Road serves the elevated strip to the west of the swamp ; to the east the main road 
follows the edge of the plain from Matamata to Te Aroha, and thence reaches Karangahake 
and Paeroa by the low Rotokohu Saddle. The Bast Coast Road runs on the lowlands 
between the mountains and the sea. This road extends eastward beyond the limits 
of the subdivision to Te Puke and Opotiki. The barriers are crossed at several points. 
Within the subdivision the only road across the Piako Swamp is that from Tahuna to 
Tirohia, complete but for a bridge across the Waihou. The Ohinemuri Valley affords a 
route across the Cape Colville Range, followed by the railway and the main road. From 
Waihi the projected East Coast Railway will follow the road through the Waiau Gorge 
to the coast. The range is not again crossed by a road suitable for vehicular traffic 
until the Wairoa River is reached. The difficult Kaimai Road follows this river in part, 
and connects Tauranga with Matamata and Cambridge. Most of this road is without the 
subdivision. The ridge between the Waimapu and Kopurererua streams is followed by the 
road connecting Tauranga and Rotorua by way of Oropi. An alternative route to Te Puke 
is afforded by the road which follows the Waitao Stream and climbs to the plateau by the 
ridge between the Waitao and its branch, the Kaiate. The saddle between Ngatukituki 
and Ngatamahinerua mountains is crossed by two bridle-tracks — the " Old Katikati " or 
" Tuahu " Track, now closed, and " Thompson's " Track, about three miles farther 
south, which is much used as a stock route. Just north of the Te Puna Creek a 
rapidly rising but well-graded road runs up to the Whakamarama Plateau. A bridle- 
track leaves this road about seven miles from the main road, and crosses the plateau 
to Okauia and Matamata. This is an old Native track — the " Tui " Track. 

A bridle-track starting from Waiorongomai zigzags up the side of Te Aroha Mountain 
to the Mangakino Saddle. The valley of this stream is followed till the Waitawheta 
is reached, when the track follows the range to the west of that river to Karangahake. 
From this track a branch track crosses the saddle to the Tui Mine, and runs down the 
range to the main road. Another track leaves a little south of Karangahake Mountain, 
and follows the Waitoki Valley to the plain. Another starting from the same point 
runs round the western face of Karangahake Mountain back to the township. 

Numerous roads leave the main East Coast Road and run to the foot of the 
range. These nearly always follow the ridges between the streams. From the end 
of the road between the Tahawai and McKinney creeks a foot-track goes to the kauii 
bush at the head of the Wairoa, and from thence, though much overgrown, may be 
followed into the head of the Waitawheta. 

Tramways have been pushed up several of the larger streams to tap the kaui'i 
and other classes of timber growing along their banks. Thus the Kauri Timber 
Company's tram from Owharoa runs for eight miles up the Waitawheta, and provides 
easy access to the head of this difficult river. The Waihi Sawmilling Company's 
tram follows the Waimata Creek for five miles, gains the hills by way of a small 
branch, and then descends to the mill at the mouth of Tamaki Creek. From the 
mill a branch runs almost to the head of the Waitanui, a distance of seven miles. An 
old tramway, still in fair order, gives access to the head of the Wharawhara Stream. 

The only port in the subdivision is Tauranga, situate on a tongue of land at 
the southern end of the shallow insilting Tauranga Harbour. To the present wharves 
the Admiralty chart of 1903 shows a channel with a minimum depth of 13 ft. at 
low water. Another wharf, close to Maunganui Mount, has been constructed in 



12 

connection Avith the railway, the channel to which has a minimum of 20 ft., this 
depth being on the sand delta outside the entrance of the harbour. Tke tonnage 
cleared in 1910 was 46,384 tons, double that of 1901. There is no oversea trade. 

Indqstries. 

introduction. 

Under this head will be considered only primary industries. The principal industries 
carried on within the subdivision are agricultural, mining, lumbering, and fishing. 
Besides the population occupied in these industries, Te Aroha Township is largely 
dependent upon the tourists who visit the springs. 

MINING INDUSTRY. 

Historical Account. 

That valuable mineral deposits occurred within the subdivision seems to have 
been indicated at a very early date. H. A. Gordon, in his inaugural address to the 
New Zealand Institute of Mining Engineers, 1897, states that ore was found on the 
ranges opposite Te Aroha between 1838 and 1840 by the late George White, of 
Whitianga. Prom this ore a small ingot of bullion was produced. The " ranges 
opposite Te Aroha " probably refers to the Hangawera Range, and not to a part of 
Cape Colville Range. 

Karangahake. 

That gold-bearing reefs existed at Karangahake was known probably as early as 
1869, but it was not until after long negotiations with the Native owners that the 
district was declared a goldfield — in 1875. The prospector's claim at Karangahake 
was situated on a great mass of slipped rock, and no discovery of lodes in solid 
country was made at this time. A twenty-head battery was erected in 1875, but 
after the first rush the camp was almost deserted until 1882, at which date all the 
principal lodes of the district were prospected. Treatment of the argentiferous ores 
of the district by the then usual wet-crushing-amalgamating method failed to give 
payable returns. The erection of a La Monte furnace at the Thames raised great 
hopes, and the Woodstock Company purchased a water-jacketed shaft-furnace which 
had been erected at Karangahake. The highly siliceous ores of the district, however, 
required the importation of suitable fluxes, and smelting was a commercial failure. 
Nevertheless, this experiment served a useful purpose in that "it was undoubtedly 
the means of opening the eyes of mine-owners to the very important fact that there 
was more bullion contained in ore generally than was dreamt of in the philosophy 
of those who were wedded to wet-crushing batteries."* 

Notwithstanding this failure, another attempt was made to treat the ores by 
smelting. A reverberatory furnace was erected to treat the ores by a method 
elaborated by Mr. Parkes, a distinguished English metallurgist. Small parcels of 
ore had been successfully treated in England, but at Karangahake the process had 
to be abandoned after a month's campaign, owing to the high cost of the necessary 
fluxes. 

Several hundred tons of high-grade ore was from time to time shipped to various 
smelting centres in Europe and Australia, but the heavy freight-costs permitted of 
only the richest ores being so dealt with. 

Pan-amalgamation was also tried about this time. A Mr. Railey erected a centrally 
situated customs plant of the type so successfully used at Washoe. This process was 

* McCombie, J. : "A Retrospect of the Ohinemuri Goldfield," New Zealand Mines Record, vol. i, 1897, p. 34. 



13 

more expensive, and saved about 45 per cent, of the assay bullion-content, but little 
more than the old battery process.* 

The cyanide process introduced in 1889, and tried here on commercial lines for the 
first time in the history of gold-mining* in connection with the Crown Mines, made 
possible the exploitation of the lower-grade ores of the district. Dry crushing, with 
roasting of the raw ore, was formerly practised preliminary to cyaniding, but the 
introduction of fine wet-crushing machinery has obviated this costly and unhealthy 
method of treatment. The progress of the district may be gauged by the accompanying 
table : — 



Year ending 


Ore crushed. 


Yield of Bullion. 


Value. 




Long Tons. 


Oz. 


£ s. d. 


March 31, 1887* 






1,186 


2,881 


6,413 




1888 . . 






623 


1,628 


4,928 Of 




• 1889 






174 


492 


4,692 Of 




1890 






449 


374 


2,600 Ot 




1891 






825 


2,032 


7,063 Ot 




1892 






460 


1,675 


5,781 




1893 






908 


4,121 


10,462 




1894 






5,200 


12,792 


25,584 




1895$ 






5,113 


15,463 


26,610 




1896 






8,055 


34,778 


37,602 12 10 




1897 






10,717 


18,091 


34,878 19 




1898 






32,542 


88,688 


90,457 16 5 




1899 






46,406 


90,204 


103,824 1 11 




1900 






54,210 


103,182 


117,714 9 11 


December 31, 1900 






34,106 


56,139 


74,360 6 1 


1901 






46,797 


62,495 


87,936 13 9 




1902 






52,886 


104,682 


104,845 10 9 




1903 






88,740 


238,666 


182.094 12 1 




1904 






71,491 


235,734 


122.823 14 1 




1905 






62,266 


281.975 


165.604 17 8 




1906 






71,653 


320,486 


192,746 8 3 




1907 






68,097 


312,371 


241,687 19 




1908 






61,338 


334,414 


244,235 1 




1909 






46,501 


294,001 


209,222 2 




1910 






51,681 


240,558 


223.565 7 5 




1911 






68,385 


240,895 


267,088 11 9 




Totals .. 






890,809 


3,098,817 


£2,594,822 1 2 



* No returns of any sort available before this, nor can any estimate be given, but the value of the bullion 
won cannot have been great. f Including value of ore sold. J For this and preceding years the 

values are estimates only. 

Te Aroha. 

The first gold discovery at Te Aroha was made by a Maori named Hone Werahiko, 
in 1879. A small rich reef was found in a gully a little to the south of Bald Spur, 
just behind the present township, at a height of nearly 1,000 ft. above sea-level. A 
rush took place. It was soon found, however, that the reef discovered was merely a 
fragment in " slip country " — i.e., fault crush— and, as nothing further of note was 
discovered, the district was deserted within six months. 

Hone Werahiko again set to work, and in the autumn of 1880 reported tlie presence 
of gold in the " New Find," and applied for various claims covering the whole of 
the Waiorongomai Buck Reef to as far north as what was to be the Premier lease. The 



* MoCombie, J. : "A Retrospect of the Ohinemuri Qpldfield," Netv Zealand Mines Record, vol. i, 1897, p. 3o. 



14 

reefs were so large and numerous, and gave such favourable indications, that great 
expectations were indulged in. The first plant was completed in November, 1883. 
" There was never a new field that had a better opportunity of being tested than 
this one, inasmuch that as soon as it was opened Messrs. Firth and Clarke erected 
one of the finest stamping-batteries in the colony, and undertook to crush the quartz 
at 10s. per ton. In order to enable the miners and claimholders to avail themselves 
of the crushing-plant, the Piako County Council, with a subsidy of £9,000 from the 
Government, constructed about three miles of tramway, at a cost of nearly £19,000, 
to connect the principal mines with the battery. When the battery and tramway 
were completed every one was under the impression that the field, opened under 
such favourable auspices, would give good returns to those who invested their capital, 
and largely increase the revenue of the county ; but these expectations were not 
realized. First one claim gave up, and then another. At the time of my visit, in 
January last, there was only one claim at work."* 

In 1888 W. R. Wilson, of Broken Hill fame, purchased the criishing plant, at the 
same time acquiring claims along the Buck Reef to as far north as Premier Creek. 
As the main reason urged for the non-success of the mines was the poor extraction 
given by the crushing plant even when the ores were roasted, the treatment-problem 
was attacked in a different way. Under the superintendence of John Howell — later 
also- well known at Broken Hill— a concentrating and smelting plant was erected. 
This plant at the time of erection was the most up-to-date reduction-works in the 
Australasian colonies, and was complete with rock-breakers, sixty head of stamps, 
Frue vanners, grinding and amalgamating pans for the tailings, revolving and rever- 
beratory furnaces to desulphurize the concentrates, and a water-jacketed shaft-furnace 
to smelt them. The whole plant cost about £20,000, and was well designed and 
built. Ore was crushed and concentrated for 3s. Id. per ton, or concentrates were 
produced for £4 9 s. 2d. per ton. The ore treated yielded by concentration about 
3 per cent, of heavy minerals. In smelting, practically all the precious metals of 
the charge were saved.| What militated against the success of the plant was the 
fact that each ton of local ore and concentrate smelted required a ton of Broken 
Hill lead-ore, as well as other fluxes. The plant was erected on the assumption that 
the Tui Mine, discovered in 1884, and known to carry large amounts of lead-ores, 
would supply part of the smelting-charge. But the Tui ore was found to carry as 
much zinc as lead, and could not be used as a flux. In 1890 part of the plant 
was dismantled, and the remaining portion and leases sold. It had been demon- 
strated that Te Aroha ores would not pay to smelt rmder the conditions existing at 
that time. 

In 1889 a pan-amalgamating plant was erected near the junction of the Premier 
Stream with the Waiorongomai. The company financing this enterprise had intended 
installing a cyanide plant, but the poor results obtained from their amalgamating 
plant deterred the shareholders from proceeding with their original plans. 

Later a cyanide plant was installed at Waiorongomai, but the considerable percentage 
of copper in the ores militated against success, although work was carried on for a 
number of years. 

In 1896 prospecting-work on a large scale was undertaken by the Colonial Exploration 
Company, and an adit along the main reef from Waiorongomai was begun.. This drive 
was eventually extended for 1,670 ft. In 1898 this company withdrew from the 
district, without taking advantage of the large amount of dead-work it had done in the 

*Goidon. H. A. : Mines Rep. 1887, p. 28. 
t Mines Report, 1890, C.-.3, pp. 43-46. 



16 

Premier section of its property. This section was afterwards worked for some years 
with great success by Mr. E. H. Hardy. 

It was about this time — 1899 — that the Rev. Joseph Campbell attempted to 
treat the refractory Tui ore, which contains large quantities of lead and zinc, by means 
of his " thermo-hyperphoric " treatment. In this process the refractory ore, broken 
to the size of walnuts and heated to a temperature of 1,200° Fahr., was subjected 
to the action of water-gas, a mixture of carbon-monoxide and hydrogen. The inventor 
claimed that refractory ore would thus be converted to a free-milling one. The Tui 
ore did not prove amenable to this process, however. 

In a previous paragraph it was mentioned that the Premier had yielded satisfactory 
returns. For several years, from 1899 to 1905, under the management of Mr. E. H. 
Hardy, the results were payable. Mr. Hardy disposed of his interests to a company, 
which has so far failed to discover another ore-shoot of any considerable size. 

The Silver King lode has lately been opened up by the Bendigo Company, and 
a battery and cyanide plant erected. The ore, however, failed to pay expenses, and 
the mine was shut down after a month's run. 

The accompanying table, compiled from official sources, shows the annual output 
of the mines of the Te Aroha area from the opening of the first treatment plant in 
November, 1883, to the end of 1911 :— 



Year ending 


Ore crushed.* 


Yield of Bullion, t 


Value, t 




Long Tons. 


Oz. 


£ s. d. 


March 31, 1884 






4,262 


4,629 


12,150 


1885 






11,042 


9,506 


24,953 




1886 






6,552 


4,489 


11,784 




1887 






4,743 


3,658 


9,602 




1888 






5,722 


2,918 


9,460 




1889 






1,381 


1,113 


2,921 




1890 






4,894 


20,416 


11,739 4 




1891 






280 


689 


500 




1892 






1,597 


979 


1,830 




1893 






1,519 


1,178 


2,350 




1894 






1,928 


2,518 


2,350 




1895J 






871 


628 


1,530 




1896 






174 


168 


470 10 7 




1897 






934 


376 


986 10 




1898 














1899 






325 


279 


834 9 3 




1900 






1,008 


753 


2,019 5 5 


December 31, 1900 






1,219 


909 


1,986 4 3 




1901 






1,289 


852 


2,384 16 5 




1902 






502 


839 


1.669 8 11 




1903 






1,561 


1,728 


4.972 18 2 




1904 






483 


281 


665 10 3 




1905 






1.727 


2.417 


6.343 16 9 




1906 






789 


875 


1,859 7 6 




1907 






, , 


, , 






1908 






, , 


, , 






1909 






5 


14 


17 10 




1910 






15 


15 


30 5 11 




1911 






750 


105 


234 15 






Totals .. 


• 


• 


55,572 


62,332 


,£116,645 12 5 



* Excluding tailings retreated. 

f Including yield from retreated tailings. 

t For this and preceding years the value given is an estimate only. 



16 

Owharoa. 
The Owliaroa district was opened to prospectors at the same time as the Karangahake 
area. As only a few of the lodes are within the Aroha Subdivision, and as the 
district has already been discussed in Bulletin No. 15, it is unnecessary to do more than 
mention the district here. 

Waitahohe. 

Gold seems to have been first reported from the Waitakohe Stream in 1895. 
Since that date the surface has been thoroughly prospected, and the Eliza reef has 
been explored by several adits and crosscuts without disclosing anything sufiiciently 
important to warrant the erection of a treatment plant. 

Mining and Treatment of Ore. 

The general rugged topography of the mining-areas within the subdivision permit 
of extensive development of the ore-bodies by means of adits alone. This is the 
only method obtaining at Te Aroha, but at Karangahake the Maria and Welcome 
lodes have been developed below the drainage-level. Of the three shafts in use there, 
all are rectangular, two are incline shafts sunk more or less along the dip of the lodes, 
while the vertical shaft is sunk in the foot-wall of the Maria lode. These shafts are 
kept open by frame - sets. In drifts the country in general requires support only 
at fault-crossings or along the lodes. 

Ventilation presents few difiiculties, and the main ventilating-current is in all 
cases produced by natural causes. At Karangahake the main currents are strong 
enough to render the carrying of an open light in them a difficult matter. In the 
Crown and Talisman mines, where air-compressing plants are part of the equipment, 
the secondary ventilation of dead ends is readily effected. In prospecting adits throughout 
the subdivision water-jets or the water-blast furnish air, through light galvanized- 
iron pipes, for long distances. 

Most of the levels have a rise of about 1 in. in 12 ft., and this is sufficient 
to carry off whatever water is encountered. Seeing that it is only at Karangahake 
that workings have penetrated below the level of the ground-water, pumping is confined 
to that area. The Crown lifts the water by an electrically driven pump, and the 
Talisman by air-driven pumps. A steam-driven pumping plant after the Cornish 
type was in course of erection in the Talisman Mine during the writer's visit. 

The ore as it is developed in the levels is sampled right across the face at 5 ft. 
intervals. Stope sampling in a systematic manner is also undertaken. 

The ore is won by the usual methods of overhand stoping ; both flat-back and 
rill stopes are used. There is no shrinkage stoping. Machine drills are used in the 
Talisman and Crown mines wherever practicable, both in development and in stoping. 
Filling the depleted stopes with waste material is universally practised, and when 
insufficient waste is derived from the breaking of the ore, " mullock rises " are driven 
in the hanging-wall. These " rises " are of the most convenient size for machine 
drilling, and are driven at an angle steep enough to permit of the broken rock finding 
its way to the stope without shovelling. Timbering in the stopes is usually confined to 
a few stuUs. 

The ore when broken in the stopes is carried to the levels beneath by the usual 
system of passes. The transport of the ore to the treatment plants will be described 
in the detailed descriptions of the mines given in another chapter. 

A summary of the methods of ore-treatment formerly in vogue has already been 
given. At the present time the treatment universally adopted consists of pulverization, 
amalgamation, concentration, and cyanidation. Pulverization is accomplished by rock- 
breakers, stamper batteries, and tube . mills ; concentration by some form of shaking 



17 

concentrator, either of the vanner or table type, blankets are also used ; amalgamation 
and cyanidation methods are essentially the same as those practised by other mines 
dealing with similar ores. A more detailed account of the ore-treatment b}' each 
mine will be given later. 

The power employed in the working of the mines is derived both from the streams 
and from steam plants. In the early days, when the lodes at Karangahake were 
worked by small companies on a limited scale, the streams afforded, as they do at 
Te Aroha to-day, sufficient power for the needs of the mining community. When 
the smaller holdings were consolidated, steam plants were installed to supplement the 
rather irregular supply of water-power. 

General Labour Conditions. 

The following extract, although written in connection with the Talisman Mine, has 
a wider application : — 

" The contract system is employed wherever possible ; one contractor, who usually 
has from six to twelve partners, will be wholly responsible for the whole of the mining 
and exploration on his particular level, with the exception of the timbering for shoots 
and leading stopes, which work is done by timber-men paid by the company. The 
contracting party may have under them some fifty men. The contractor obtains 
his steel, dynamite, candles, &c., from the company ; and these, plus drill-sharpening, 
repairs, breakages, depreciation of hose, loss of steel, &c., are entered as a contra 
to his account. The contractor delivers the ore at the ore-hopper of his level, 
and the tonnage is estimated by counting the number of skip-loads received when 
hauling from there to No. 8 level. Payment is made on this tonnage, which is checked 
by the number of truck-loads taken out by the horse-tram to the aerial ropeway. 

" In driving, rising, or sinking payment is made per foot of progress, and if the 
material excavated is sent to the mill, payment is then made at an alternative price 
per foot, which is included in the original tender. 

" The filling of stopes is done by the same contractor, and timbering — such as cribbing 
of passes and manways, and stulls to support weak hanging-walls — is paid for separately 
at per running foot and per stull. 

" When sets are required for drives, or framed sets for winzes or rises, payment 
is made for their erection at per set."* 

Since the above was written a sort of co-operative system of contract has been 
introduced, by which each workman employed is a participant in the contract. The 
other mines have adopted slightly different systems, according to the requirements of 
local conditions. 

The larger mines occasionally let tributes to small parties of men, who exploit 
portions of the workings abandoned by the companies. The conditions of the tributes 
vary according to circumstances. 

Financial Conditions. 

All the area within which the lodes occur in the Aroha Subdivision belongs to 
the Crown or to Native owners. Under certain conditions companies, syndicates, or 
individuals may lease these lands and work the lodes. The gold won is subject to a 
tax of 2s. per ounce, 992 line. An additional tax of 3(1. per ounce has recently been 
imposed in connection with the Gold-miners' Relief Fund. 



* Jannan, A. : " Mining and Ore-treatment at the Talisman Mine, Karangahalte, New Zealand," Trans. 
Aust. Inst. Min. Eng., vol. xvi, 1912, p. 359. 

2 — Aroha. 



18 

In the early days of mining only small areas could be leased, but now it is 
recognized that larger areas must be granted if the investor is to have a fair chance 
of being repaid the heavy expenditure for the plant and development of the modern 
mine. Thus, the two large English companies operating at Karangahake — the Talisman 
and the Crown Mines — hold areas of 507 acres and 404 acres respectively. 

AGRICULTURAL INDUSTRIES. 

The main portion of the inhabitants of the subdivision rely on agricultural industries 
for a livelihood. These industries include dairy-farming, raising and fattening stock, 
horse-breeding, the growing of cereals, root-crops, vegetables and fruit, and viticulture. 

Dairy-farming has of recent years made great strides. The light soils of the 
Hauraki Plain and the Katikati Lowlands when suitably manured have been found 
to form admirable grazing land. The fairly even distribution of the rainfall throughout 
the year maintains a steady plant-growth, and the mildness of the climate permits a 
long milking season — from October to May. There are central butter-factories at 
Katikati (Waitakohe Stream) and Tauranga on the eastern side of the range, and 
at Paeroa, Waihou, and Manawaru on the western side. Numerous creameries supply 
these factories. There is still room for much expansion in this industry, especially 
on the Tauranga side of the range, where great tracts of rolling country suitable 
for grazing may at present be designated waste land. 

Cattle-fattening and horse-breeding have their centre a little to the south of 
Te Aroha ; while sheep thrive well on the dry pastures found on the peninsulas jutting 
into Tauranga Harbour. 

The growing of cereals (chiefly oats and maize) and of root-crops (mangels and 
turnips) is mainly as an adjunct to dairy-farming. Garden-produce grown in the 
Katikati district finds a ready sale in the Waihi market. The same may be said of 
a large proportion of the fruit grown in that district. Apples, pears, plums, peaches, 
and lemons thrive here. In the writer's opinion fruit-growing will become one of 
the staple industries of the country on the eastern side of the range, once reliable 
transport for the fruit can be obtained. 

Viticulture and wine-making are practised to a limited extent. The grapes grown 
are mostly American varieties. The wine produced is a sweet still wine of excellent 
body and flavour. The yield is from 250 to 400 gallons per acre, according to the 
season. 

THE TIMBER INDUSTRY. 

There are three companies engaged in the timber industry within the Aroha 
Subdvision — the Kauri Timber Company, the Waihi Gold-mining Company, and the 
Waihi Sawmilling Company. The Kauri Timber Company's bush is at the head of 
the Waitawheta. A well-graded iron tramway runs from Owharoa to the bush, a 
distance of seven miles. Kauri is the only timber cut, and the timber is so valuable 
that the scarps are sawn, not chopped. The logs are hauled to the tram-line by 
steam-haulers, loaded on the company's trucks, and drawn by horse to Owharoa, 
where they are transferred to railway-wagons and taken to Paeroa. From this point 
they are rafted to the mill on the Great Barrier Island. 

The Waihi Gold-mining Company draw the timber required in their operations 
from the Waitawheta bush also. They use the Kauri Timber Company's tram for 
the haulage of the timber, and have a branch line running to the Victoria Mill at 
Waikino. 

The Waihi Sawmilling Company have their mill, which is driven by steam, in the 
Tuapiro Valley, at the junction of the Tamaki Stream. The milling-timber in the 



19 

valleys of the Waitanui and Tamaki has been cut out to a great extent. The logs 
were transported to the mill in the case of the Waitanui by a wooden-railed tramway; 
in the case of the Tamaki they were " driven." The timber is now chiefly drawn 
from the head of the Wairoa Stream. Transport is effected by " driving." Large 
dams have been built in the two head branches of the Wairoa. The logs are hauled 
to the creek by bullock-teams, and after heavy continual rain the dams are " tripped." 
The logs are carried downstream by the great flood of released water, and are caught 
in booms erected at the mouth of the stream. This method of transport cannot 
be considered economical. A large proportion of the logs are smashed to splinters 
against the rocks as they tumble over the falls and rush through gorges. The sawn 
timber is taken by horse-haulage over a wooden-railed tramway eight miles in length 
to the timber-yard near Waihi. 

In the valley of the Wairoa Eiver, near Tauranga, rimu and totara are being 
milled. The sawn timber is towed by oil-launch to the mouth of the river, and is 
there loaded into scows. 

The bush on the Whakamarama Plateau is likely shortly to be attacked by a 
sawmilling company. It contains large quantities of rimu, and also totara, black-pine, 
and mangeao. 

At one time Cashmore Bros, had a mill in the Wharawhara Valley, but all the 
kauri has now been cut out from this portion of the range, nor can lumbering operations 
continue for more than a few years in any part of the subdivision. 

THE FISHING INDUSTRY. 

The fishing-grounds of the Bay of Plenty are likely in the future to be much 
more extensively exploited than they are at present. As Tauranga Harbour is the 
only safe port on the shores of the bay, the fishing industry will have its headquarters 
there. At present most of the fishing is in the hands of the Maoris, with Tauranga 
and Te Ho as the centres of operation. 



20 



CHAPTEK III. 



PHYSIOGRAPHY. 



General Features 

Mountains . . 

Plains 

Rivers 

Rivers of the Hauraki Plain 

The Ohinemuri River 

Other Branches of the Waihou 

Streams draining to the Bay of Plenty 

Waterfalls . . 



Page 
20 
20 
20 
21 
21 
21 
23 
23 
23 



Swamps, &c. 
The Coast-line 
Tauranga Harbour 
Islands 
Springs 
Influence of Man 

Deforestation 
. Drainage of Swamps 

Conclusion 



24 
24 
25 
25 
26 
26 
26 
28 
28 



General Features. 

The principal physiographical feature in the Aroha Subdivision is tlie Cape Colville 
Range. This maintains a general north-north-west direction throughout the subdivision. 
On the eastern side the range is separated from the Bay of Plenty by a strip of 
lowlands of variable width. On the western side occurs the Hauraki Plain, which, 
within the district, maintains a width of about ten miles. The Hangawera Hills, 
a range of low hills, bound the plain on the western side. 



Mountains. 

The highest peak in the district — and, indeed, of the whole range — is Te Aroha 
Mountain (3,126 ft.). A ridge about six miles long, averaging 1,200 ft. in height, 
connects Te Aroha and Karangahake mountains, the latter a prominent peak (1,775 ft.) 
overlooking the gorges of the Waitawheta and Ohinemuri rivers. Eastward of Te Aroha 
Mountain, and separated from it by the profound gorge of the Waiorongomai, is the 
plateau-like mass of Ngatukituki. Prom this plateau northward, long gradually 
dropping spurs descend to the Waihi Plain. South of Ngatukituki the range is 
reduced to a single ridge, with remarkable knobs occurring at subequal distances along 
it. This ridge, which is three miles in length, gives place to the high Ngatamahinerua 
Ridge, which maintains a height of 2,700 ft. for over three miles. South of this 
mountain - mass is the Whakamarama or Whanga Plateau, which rises gently from 
a height of 1,200 ft. under the shadow of Ariariparitapu, the southernmost peak on 
the Ngatamahinerua Ridge, to 2,531 ft. at Te Weraiti, ten miles to the south and 
three miles beyond the southern boundary of the district. 

The Hangawera Hills, on the west of the Hauraki Plain, are nowhere more 
than 800 ft. in height. Northward, beyond the district, these hills are continued as 
the Pateroa Range. 

Plains. 

The largest area of flat land within the subdivision is the Hauraki Plain. This 
extends north and south many miles beyond the boundaries of the district. It is a 
plain of recent aqueous deposition ; and as the rivers of this plain — the Waihou, Waitoa, 
and Piako — have their basins essentially ydthin the plain itself, it is impossible that 
they alone were concerned in its formation. This, however, is a question which will 
be discussed on later pages. 



21 

The Katikati Lowlands form a strip of varying width, between the mountains and 
the Bay of Plenty. They are but the remnants of a much more extensive area of 
low-lying country. The sea has been the destroying agent, and is still actively removing 
such portions as are exposed to its attack. 

The Waihi Plain, about thirty square miles in area, is remarkable in that it is 
surrounded by hills, that recent water-borne deposits are almost entirely absent, and 
that its drainage escapes by a deep caiion to the west, although there are at least 
three easier routes to the sea on the east. The history of this plain is connected 
with that of the Ohinemuri River. Its formation will be discussed in the next section. 

Rivers. 
The Rivers of the Hauraki Plain. 

The most considerable river in the subdivision is the Waihou, or Thames. This 
river has its main valley entirely within the Hauraki Plain, yet it does not wander 
-widely across the plain until near the junction of the Ohinemuri, beyond the northern 
limits of the subdivision, and sixteen miles from the sea. Within the Aroha Subdivision 
for a distance of twenty-seven miles in a straight line the narrow meander belt of this 
river maintains a relatively straight course, at an average distance of only 100 chains 
from the range. This meander belt, which has a width of 35 chains below Te Aroha 
and a deptli of 25 ft. below the general level of the plain, gradually narrows and 
deepens, until near Ramaroa, on the southern boundary of the subdivision, the belt is 
20 chains wide and the river 70 ft. below the surface of the plain. At this place there 
are traces of an older and wider meander belt on the plain. Within the main meander 
belt there is abundant evidence of the downstream migration of the meanders,* not- 
withstanding that the meanders are entrenched to some extent. At Ramaroa the river- 
surface is 60 ft., at Te Aroha 26 ft., and at Paeroa not at all above high-water mark. 

The other rivers of the Hauraki Plain — ^the Piako and its branch, the Waitoa — 
also have their basins almost entirely within the plains. These, although smaller rivers 
than the Waihou, nevertheless wander more widely. Thus the Waitoa has between 
Tatua and Waitoa railway-stations a much wider valley than the Waihou. The 
physiography here indicates that at one time a much larger river than the present 
Waitoa flowed in this wide valley. 

The Ohinemuri River. 

This is the largest tributary of the Waihou. Its confluence with the- Waihou is 
without the Aroha Subdivision, but the larger part of its basin is within. xA.t the 
junction the Waihou is much farther from the range than is usual. The minimum 
summer flow of the Ohinemuri at Paeroa is about 50 cubic feet per second. The Ohine- 
muri drains the Waihi Plain, a relatively level tract of land seven miles long by four miles 
wide. The hills to the east and south-east rise with subdued topography from the 
plain ; and here also the major streams flow in wide mature valleys, while the brooks are 
lost in swamps. The Ohinemuri itself rises without the subdivision, so that in following 
the river downstream the Waione Creek will be, for the purposes of this description, 
considered the headwaters. This stream, from its source in the mature hills to the 
east of Waihi, flows in a wide swampy valley showing all the signs of old age. On 
entering the plain the swamps increase in size, each little branch is enveloped in 
creeping morass, and the watersheds separating the streams are but a few feet above 
the valley-floor. Near the junction with the Ohinemuri at Black Hill the fall increases, 
and the Waione enters the main stream by a narrow ditch. The Ohinemuri itself 



* See plan p. 29. 



22 

here flows entrenched in the so-called Waihi Plain, which is in reality, however, an 
open mature river-valley, on the gently sloping flanks of which the Town of Waihi is 
built. As the river is followed down, the juvenile banks increase in height, major 
streams like the Waimata and Mangakiri join it at grade by miniature caiions, but the 
brooks enter the entrenchment by waterfalls, which increase in height downstream. 
Between Waihi and Waikino, on the north side of the river, the Ohinemuri and its 
branches have cut out hills of circumdenudation in the relatively soft pumiceous tuff. 
Just above Waikino the Waitekauri comes in at grade from the north, whilst at 
Owharoa the Tieri tumbles over a 40 ft. waterfall a few chains from its junction with 
the Ohinemuri. Below this the valley widens, and some small creeks join it at grade, 
but here the rocks are greatly crushed. Soon the river enters a narrow caiion, the 
vertical walls of which tower 600 ft. above the stream now boiling amid great rocks. 
At Karangahake the valley opens out a little, but still remains a steep-sided V-shaped 
valley until its embouchure on to the Hauraki Plain. At Karangahake the Ohinemuri 
is joined by the Waitawheta, a river of almost equal size. This stream, from a wide 
mature middle valley in which it has entrenched itself, cuts through a spur of Karanga- 
hake Mountain by a canon similar to that of the Ohinemuri. It is believed that the 
peculiarities of the topography of the basin of the Ohinemuri are due to an elevation 
of the whole basin, combined with a tilting movement to the east. The Ohinemuri and 
the Waitawheta have maintained their courses across the maximum uplift of the western 
edge of the elevated earth-block. They are therefore antecedent streams which had, 
before the elevation, escaped from the hills by the wide mature valley which shows at 
Karangahake about 700 ft. above the present streams. This ancient valley had here a 
width of 120 chains, and extended from the present Waitawheta Gorge to the Rahu 
Saddle. There is a steady slope of hill-crest and plain from this ancient valley, which 
. stands at a height of 800 ft. above sea-level, to the eastern end of the Waihi Plain 
(360 ft.), eight miles away. Assuming, as may reasonably be done, that before the 
commencement of this uplift the Ohinemuri discharged into the sea, which at that time 
occupied the Hauraki Plain, and that the grade of the mature Ohinemuri was 10 ft. per 
mile, it is found that the uplift on the west of the earth-block is at least 550 ft. more 
than at what is now the eastern end of the Waihi Plain — i.e., the saddle to the Waiau. 
It would be but natural that in consequence of this tilting movement readjustments in 
drainage should have taken place. These readjustments should have affected the eastern 
side of the basin of the old Ohinemuri, especially as elevation would have rejuvenated 
the streams . draining eastward to the sea. It is believed that the Wairoa, Waitanui, 
and Tamaki, which unite to form the Tuapiro, flowing by a deep juvenile gorge to 
Tauranga Harbour, once formed the headwaters of an eastern branch of the Ohinemuri, 
comparable in size with the present Waitawheta. This stream once flowed northward 
to the west of Hikurangi Mountain, in a valley which may still be traced. The Tuapiro 
has not been the only stream to benefit by the weakness of the Ohinemuri ; the Waiau 
has broken into and captured part of the drainage of the ancient basin. Farther north 
the small stream down which the road to Waihi Beach takes its way, and also the Waihi 
Stream, have now cut through the eastern hills and reached the plain. Other writers — 
Park,* Cheal,t Lindgren,J Bell and Fraser§ — consider that at one time the Ohinemuri 
flowed to the Bay of Plenty. 

* Park, J. : " Geology and Veins of the Hauraki Peninsula," Trans. N.Z. Inst. Min. Eng., vol. vii, 1897, 
pp. 84 and 90. 

t Cheal, P. E. : Discussion of previous paper, op. cit., pp. 120-21. 

J Lindgren, W. : " The Hauraki Goldfields, New Zealand," Eng. and Min. Jouin., vol. Ixxix, 1906, 
p. 218. 

§ Bell, J. M., and Fraser, 0. : Bulletin No. 15, 1912, p. 32. 







Si! 

si, 






(55 
'si 



23 

Other Branches of the Waihou. 

It is impossible to enumerate all of these ; and only such as are of considerable 
size, or are otherwise remarkable, will be mentioned. • 

The Waiorongomai has cut a deep gorge to the east of Te Aroha Mountain, and 
flows southward, directly contrary to the course of the Waihou. 

The Wairakau and Waipupu drain steep slopes by numerous branches. The Wai- 
harakeke, Maungapukatea, and Parengorengo are similar streams. 

The Wairere and Waiteariki are remarkable from the great waterfalls which occur 
in their lower courses. Their main basins are on the Whakamarama Plateau, about 
1,000 ft. above the Hauraki Plain, and the lower courses of the streams are so youthful 
that only slight notches have yet been cut in the great wall which here bounds the 
plain on the east. 

Considering the branches of the Waihou as a whole, they show a progressively 
younger topography from north to south. Thus the streams to the north of Te Aroha 
have valleys much more mature than those between Te Aroha and Ngatamahinerua 
mountains, while these in turn are less youthful than those of the Wairere and Waiteariki. 

Streams Draining to the Bay of Plenty. 

In proceeding from north to south the first "stream of note is the Waiau. This 
stream flows into Tauranga Harbour from a narrow recent valley which takes a 
remarkable right-angled turn in the middle of the hills. It alters its course abruptly 
again when its upper basin, pirated from the Ohinemuri, is reached. 

The next stream is the Tuapiro, the history of which has already been sufliciently 
indicated. 

The Wharawhara, Eere-atu-kahia, and Waitakohe have upper courses controlled by 
structural features. The same may also be said of some of the branches of the 
Aongatete, the Kauritutahi, and Poupou. 

The upper Aongatete, Whatakao, Wainui, Waipapa, and Te Puna constitute a group 
of streams of common origin. All have their upper courses in the Whakamarama 
Plateau, the surface of which slopes gently northward, finally merging into the coastal 
lowlands. The wandering nature of their upper courses, the straight, narrow, rapidly 
descending valleys of their middle courses, and the northward- sloping, even-crested, 
intervening ridges suggest that these streams are consequent to the elevation and 
northward-tilting of a base-levelled earth-block. Of the other sti earns which drain into 
the Tauranga Harbour — the Wairoa, Kopurererua, Waimapu, and Waitao — only the 
lower courses run within the area examined. The Wairoa is a large stream, second in 
importance — as far as the Aroha Subdivision is concerned — only to the Waihou. 

Waterfalls. 

These are exceedingly numerous ; at the heads of almost every stream within 
the mountains waterfalls occur. Many of the streams draining from the steep western 
flank of the range from Te Aroha southward have courses consisting of a series of waterfalls 
and rapids. The most noteworthy falls on this side of the range are those of the 
Wairere and Waiteariki. The white column of the upper fall of the Wairere is a 
landmark for many miles. The total height of the two leaps is 360 ft. The falls 
'of the Waiteariki are invisible from the plain, and not so well known as those of the 
Wairere. The two main falls have a total height of 260 ft., but, although the stream 
carries at least double the quantity of water of the Wairere, the falls are not nearly so 
impressive. 



Plate IV. 




Maunganui, froji I'auraisiga Spit. 




Monmouth 1\Edoubt, Taukanga. 



t/eo. Bull. No. 16.] 



ITo face p. 25. 



25 

Tauranga Harbour. 

This shallow inlet is hfteen miles in length. The depth of water over the greater 
portion of its area is small, but tidal scour maintains deep channels at both the 
entrances. Inlet deltas are shown by the Admiralty charts to have formed at the 
mouth of each entrance. The currents with each rising tide carry into the harbour 
a burden of sand, which is deposited when the currents ' lessen ; the outgoing tide 
carries out of the harbour an approximately equal burden of sand, which is deposited 
in the form of an inlet delta outside the entrance. Like river deltas, these deltas 
have several channels, and of these the central one is the chief. The eastern side of 
the inlet is formed by Matakana Island, which is divided into two portions. The inner 
portion, or Matakana proper, is formed of subaqueous sands and silts, and is separated from 
the sandspit portion (Panipaui) by a swampy depression. Along the western shore of the 
inlet occur numerous estuaries and bays. Each stream, no matter how small, has its 
widely flared mouth. Tidal currents are planing away the points of land and filling 
in the bays. Tidal erosion has cut away from Omokoroa Point 6 ft. in forty years,* 
and on Matakana Island the erosion is even more rapid. 

The facts that each stream-valley opening to Tauranga Harbour is now invaded by 
the sea, that swamps filling the lower courses point to a time when the sea once 
penetrated farther into the land, that the slope of the banks bordering these swamps 
is quite abrupt, and that the stream-valleys immediately above the swamps have all 
the appearance of youth, all suggest a recent drowning of the valley-mouths by a 
positive movement of the strand-line. 

Again, these drowned valleys seem to converge in a manner suggesting that at 
one time the streams united to form two rivers flowing to the sea, the one a little 
south of Te Ho, and the other north of Maunganui. Submergence drowned these streams 
and the sea penetrated into the land, ramifying according to the distribution of the 
valleys. It is for this reason that the veriest trickle draining to the harbour direct 
has an estuary. It is not unlikely that immediately after the subsidence Matakana 
proper had land-connection with Omokoroa Point, and that the present channel has 
been formed by tidal erosion. It is possible now to wade to Matakana Island from' 
Omokoroa Point at low water. 

The following table contains the information available in connection with the tides 
of Tauranga Harbour and neighbouring ports : — 





High Water, 


Full and Change. 
H. min. 


Spring Rise 
Ft. in. Ft. 


in. 


Neap Rise 
Ft. in. Ft. 


in 


Coromandel 




.. 7 20 


11 


Oto 12 





9 




Tauranga 




.. 7 20 


5 


6 to 7 


6 


5 Oto 6 





Omaru Bay 




.. 6 43 


6 


Oto 8 





5 Oto 6 





Hicks Bay 




..7 


6 


6 to 7 


6 


5 6 to 6 


6 


Open Bay 
Tolago Bay 
Gisborne 




.. 6 38 
.. 6 10 
..6 8 


8 
7 
6 




Oto 8 
Oto 7 




(1 


6 Oto 7 
6 to 7 
5 







Islands. 
These are of two types — those wiiich liave been formed from prc-e.xisting 



and. 



and those which have been built up by wave and wind action from material supplied 
by the sea. To the first type belong To Karewa and Motu Otau, both rhyolite 
fragments. Te Karewa is about seven miles north-north-west of Maunganui Mount, 



* loformatioa from Captain Arthur Crapp, Omokoroa Point. 



26 

and about three miles and a half from Matakana Island. It is a mere rocky islet. 
Motu Otau, about a mile to the east of Maunganui Mount, is separated from the 
sandy beach by shallow water. The writer believes that the sea is gradually building 
up the beach, and that in course of time Motu Otau will be connected with the 
mainland by a sandspit. Motu Otau will then be exactly comparable with Moturiki, 
a rhyolite-tipped peninsula between Maunganui Mount and Motu Otau. Maunganui 
Mount and Te Ho are similarly believed to have once been islands, though now joined 
to the mainland by sandy isthmuses. 

Other residual islands cut by the sea from the soft sands and silts of which the 
Katikati Lowlands are formed are Matakana proper and Motuhoa. Tutaitaka, Motuopui, 
and a few other islets in Tauranga Harbour have a similar origin. 

Of accretionary islands, the largest — Panipani — forms part of Matakana, and is separated 
from Matakana proper by a low swamp. Panipani is about fourteen miles long and 
a mile wide, and is traversed longitudinally by parallel sand-dunes up to 50 ft. in 
height. These dunes are well covered by vegetation, and between the ridges are narrow 
swampy pastures. 

Te Hopai, a low swampy island at the mouth of Opui Creek, has been built up 
by tidal currents depositing mud among swamp plants in a sheltered corner of Tauranga 
Harbour. Other islets in Tauranga Harbour have a similar origin. 

Springs. 

The springs of the Aroha Subdivision may be divided into two classes — (a.) Cold 
springs, obviously dependent upon surface-waters. (b.) Mineral springs, not obviously 
dependent upon surface-waters. 

Springs of the first class are to be found at the head of every streamlet and 
along the flanks of every valley. They form the sources of all streams, and usually 
have individually a very small flow. The numerous springs issuing from the talus 
slopes along the western escarpment of the range belong to this class. Two large 
gushing springs in the valley of the Whatakao are obviously fed through fissures 
in the rock by the waters of the stream above the falls, near the bottom of which 
the springs issue. 

The springs of the second class are a valuable asset to the district. They are 
so numerous and important that a separate chapter has been devoted to their discussion. 

Influence of Man. 

Man, in reducing a new country to supply his material needs, alters the nice 
balance of forces that exists in nature ; and when one of the factors involved is disturbed 
it is hard to say how far the effect may reach, or when stability under the new 
conditions will be established. Among the first works undertaken by man in a new 
country are the removal of the forest and the drainage of the swamps. 

Deforestation. 

The forest represents the highe'st development attainable in the vegetable kingdom. 
Not all land can support forest-growth, and forest-trees can grow usually only after long 
preparation of the soil by smaller plants. The soil of a forest is rich in moisture- 
retaining nitrogen-bearing humus. It is covered by a carpet of leaves and twigs in all 
stages of decay, which retards evaporation and conserves moisture, ultimately to be 
transpired by the leaves, for the solution of plant-food. 



27 

The clearing of the forest, when conducted under the most favourable conditions, 
involves first the removal of the larger trees for milling purposes. In the hilly portion 
of the subdivision the lumberman builds dams at the heads of the creeks, and creates 
artificial floods, by which logs, dragged to the creeks, may be transported. During a 
" drive " the logs, driven by the rush of the waters, scour out the bottoms of the creeks 
in a way no natural flood could do. When the milhng-timber has been removed the 
undergrowth is cut down and, when sufficiently dry, is burned, the fire kdlhng any 
large trees still standing. Grass-seed is then sown, and the land is stocked. Later the 
unburned wood is " logged up " and burnt, and in due time after the decay of the 
roots, the land, if not too steep, is brought under the plough. Often, after the first 
burning, fern, tea-tree, or wineberry take possession of the land, necessitating further 
burning, perhaps many times repeated. By each burning, but especially by the first, 
a large proportion of the humus is destroyed. Thus the soil loses not only a large 
amount of valuable nitrogen, but also in part its power of resisting drought. The soil 
is less fertile after the destruction of the forest. In the economy of nature deforestation 
must be regarded as a retrograde step. 

Another bad effect of deforestation is that the soils, dry and pulverulent after 
burning, are readily carried away either by wind or rain. A variable proportion of 
such transported soil finds its way to the sea, and is lost. Again, much of the valuable 
potash and phosphorus of plant-growth contained in the ashes from a " burn " are 
dissolved and carried away before they can be utilized by further plant-growth. 

Again, on hill-slopes, after deforestation and the rotting of tree-roots, sUps of 
greater or less magnitude are of frequent occurrence. 

When a whole region is cleared the effects of deforestation so accumulate as to be 
plainly appreciable. The mountain valleys are filled with debris. The streams, no 
longer fed by the gradually discharging forest-reservoirs, are dry stony gullies in fine 
weather, while during rain they are filled with tempestuous torrents, carrying loads of 
gravel to the plains. There they constantly change their courses, and convert fertile 
land into stony wastes. The finer grits and sands are carried to the trunk streams, 
there to fill in the channels, while the soil, the wealth of the hills, is carried to the 
sea to be lost for ever. The effect of wind must also be considered. A clearing in a 
forest is protected from heavy winds. The warmth-exhahng forest mitigates the frosts 
of winter, and everything is in favour of plant-growth. Later, when the protecting 
forest has been destroyed the land is exposed to the fierce heat and scorching winds of 
summer, and the bhghting frosts and bitter storms of winter. 

Hitherto the writer has confined himself strictly to well-proven facts, but there is 
another eftect of deforestation which, from its very nature, does not lend itself to 
scientific demonstration — secular change of climate. It must be admitted that rainfall 
observations over regions which have been deforested within recent times show that the 
rainfall is apparently but httle affected. On the other hand, the trees planted in 
Egypt since the British occupation have certainly had some effect upon the rainfall. 
That many regions where arid conditions now obtain were at one time heavily forested 
is well known. Such were Persia, Mesopotamia, Palestine, Sinai, and, indeed, many regions 
bordering the Mediterranean. Whether the change of chmate which produced this 
aridity was brought about by the deforestation, or was merely coincident with it, is an 
open question. Certain it is, however, that by irrigation the plains of Mesopotamia 
fed vast populations until the floods of the Tigris and Euphrates became uncontrollable, 
consequent on the deforestation, by man, of the Armenian plateau. 

Another class of country occurring within the subdivision has been })rejudicially 
affected by man's occupancy. The sand-dunes of the east coast occupy a considerable 



28 

area. Originally they were covered by heavy forest, much of which was probably 
destroyed by the fires of the aborigines. Later they were covered by scrub. This 
has now been largely removed, and the dunes grassed and stocked. Unfortunately, 
in places the dunes are no longer fixed. Thus north of Te Ho the sand is 
rapidly advancing inland, and already at some points has reached the Opawe Swamp. 
There is clear evidence at this pla' e of an increasing area being occupied by migrating 
dunes. Cattle and sheep have also at some places broken the layer of sandy loam 
covering the dunes, and exposed the sand beneath. This is true also of the fixed dunes 
of Matakana Island, although here the dunes are, as a whole, well covered. 

Drainage of Stva^nps. 

The principal swamps within the Aroha Subdivision are those of the Hauraki Plain. 
The subsoil of these swamps is clays and uuconsohdated pumiceous sands. When a 
swamp is drained the swamp vegetation dies, the peaty soil contracts, and the surface is 
lowered many feet. The surface vegetation is usually burned off ; but this must be 
done before drainage has proceeded too far, otherwise the peaty soil itself may burn, 
and the surface may be lowered to such an extent that, when the unburnt portion 
contracts, the area may be subject to floods. Again, much of the marshy lands of the 
Hauraki Plain, especially above Te Aroha, Avhere the rivers have entrenched themselves, 
is well above the drainage-level of the plain, and requires but small ditches to drain it. 
The pumiceous sands underlying the surface are so incoherent that, if there be much 
fall, a deep wide channel is soon cut. Near the Waihou River some of these ditches, 
which were originally 5 ft. drains, are now more than 20 ft. deep, over 2 chains wide, 
and many chains in length. All the material from these great excavations has found 
its way into the river. Moreover, these gulches must be expected to increase in size ; 
and any drain similarly situated, cut in the future, must be expected to excavate a 
similar channel unless the outfall be specially protected. 

Conclusion. 

In the foregoing paragraphs only the unfavourable effects of man's occupancy have 
been noticed, in the hope that attention may be drawn to the subject and remedial 
measures adopted. The writer beheves that rough broken country is, apart from the 
aesthetic point of view, of more value to the commonwealth when forested than when 
covered with bracken and scarred with sUps, and for this reason would urge that the 
indiscriminate burning of bush, or even scrub, in such locahties by irresponsible persons 
be stopped. In such a locahty as the Whakamarama Plateau, which is still for the 
most part heavily forested, such clearings as do exist carry most luxuriant pasture. 
The rock from which the soil has been formed is the same as that underljdng the 
barren higher portions of the Katikati Lowlands. It seems advisable that belts of 
forest should be left upon this high-level rolhng country to act as wind-breaks. The 
necessity for such wind-breaks has been amply demonstrated upon the Hauraki Plain 
and the Katikati Lowlands. The need for care in the treatment of sand - dunes is 
recognized in all civihzed countries. For a discussion of the treatment of sand - dunes 
in New Zealand, see Dr. Cockayne's report.* 

In regard to the silting-up of the channel of the Waihou River, which is a very real 
evil, obstructing the navigation of this valuable waterway and causing the low-lying 
lands to be subjected to disastrous floods, the popular behef is that the trouble is 
due to the discharge of battery taihngs into the Ohinemuri and, to a less degree, to 

* Cockayne, L. : " Report on the Dune Areas of New Zealand," Department of Lands, 1911, C.-13. 



29 



the growth of the willows along the river-bank. Other factors, however, also operate, 
and must not be overlooked. Of these the principal is the increased load of sediment 
brought from deforested hills and unprotected swamp drains. So bad has the silting 
evil become that the authorities are now, at great expense, removing the willows, and 
intend to shorten the course of the river where practicable. Cultivation always 
increases the amount of sediment discharged into streams — that is, increases the rate of 
denudation — and, in low plains drained by sluggish rivers, silting is hable to follow man's 
occupancy. Thus, when the Hauraki Plain is more closely settled the Piako may be 
expected to fill in, just as the Waihou has done, although no battery taiUngs have 
been or are hkely to be discharged into it. 

One other point in connection with floods is worthy of notice. The reservoir 
effect of forests has been pointed out ; swamps and swamp growth have a similar 
storage-power. Before forests are cleared or swamps drained consideration must be 
given to the total annual run-off of the area affected, and the capacity of the channels 
of the rivers, and whether the channels have sufficient capacity to cope with the 
increased maximum floods which will follow upon the clearing of forests and the draining 
of swamps. If the channels are unable to cope with the increased maximum floods, 
then clearing and draining will merely bring about an exchange of land-values, in that 
creation of farm lands in the upper portion of a river's basin will be followed by 
destruction of land in the lower valley. 




/' /' 




Courst according to aid Sunt^ 

. late // 




Plan showing Migration of Meanders of Waitiou River. 



30 



CHAPTER IV. 



INBRAL SPRINGS. 



Te Aroha Group of Mineral Springs . . 30 
Okauia Group of Mineral Springs . . 36 

Waitoa Group of Mineral Springs . . 37 



Katikati Group of Mineral Springs . . 39 
Origin of Mineral Springs . . . . 39 

Conclusion . . . . . . . . 45 



The mineral springs of tlie subdivision may be divided, according to geographical 
distribution, into four groups — (a) Te Aroha group, (b) Okauia group, (c) Waitoa group, 
(d) Katikati group. 

Te Aroha Group of Mineral Springs. 

The Te Aroha group of mineral springs is situated at the base of Te Aroha 
Mountain, the steep wooded face of which, rising abruptly immediately beside the 
springs, is, as will be pointed out on a later page, a great fault - scarp. Through the 
crushed rock due to this fault-zone arise the springs, which occur over an area about 
25 chains in length, in the northern portion of which the springs are warm, in 
the southern cold. The northern portion has been set aside as a domain, mthin 
which bath-houses and swimming-baths have been erected, tennis-courts and bowHng- 
greens constructed, flower-beds and shrubberies laid out, while easy paths wind through 
plantations of native and foreign trees to the graded track leading to the summit of 
Te Aroha Mountain. The willow-fringed Waihou, flowing through the town, affords 
fishing and boating. Nature and man have combined to make Te Aroha the most 
beautiful spa in the North Island, where the invahd may find health, and the general 
visitor spend a deUghtful holiday. 

The waters of Te Aroha are justly famous for their therapeutic properties. Quite 
recently the water from some of the cold springs has been put on the market under 
the name of the " Waiaroha Mineral Water." 

A plan has been prepared showing the position of most of the springs. Two 
tables have been compiled containing the pubhshed analyses of the waters from the 
Te Aroha springs (see pp. 32-35). Concerning the alkaUes contained in these waters, 
it may be said that potash exists in all of them, and that hthia has been found when- 
ever sought. 

In 1910-11 Dr. J. S. Maclaurin, of the Dominion Laboratory, investigated the 
radio-activity of some of the thermal waters of the North Island. For the Te Aroha 
springs his results* were as follows : — 







Radio-activity. 


Radium-content. 


Source. 


Temperature, °C. 


Radium. 


Radium. 






Grams, x 10~ per c.o. 


Grams, x 10 per c.c 


No. 2 Spring 


38° 


0-026 


0-0009 


No. 6 „ 


35° 


0015 


0-0002 


No. 8 „ 


42° 


0-010 


0-0010 


No. 15 „ 


50° 


0-031 


0-0012 


No. 20 „ 


18° 


0-056 


0-0005 


No. 22 „ 


21° 


0-130 


• • 



* Dominion Laboratory : 44th Annual Report, 1911, pp. 68, 69. 



31 

It will be noted tliat the cold springs Nos. 20 and 22 are much more radio- 
active than the warm springs ; and in view of tlie fact that the rocks in the vicinity 
of the surface of the earth are much more radio-active than the deep-seated rocks,* 
this greater radio-activity is of significance when the origin of the springs is 
considered. 

Concerning the medicinal properties of the waters of the Te Aroha springs, 
Dr. Wohlmann,f Government Balneologist, writes : — 

" The thermal waters may be classed as muriated alkahne. As will be seen from 
the subjoined analyses, the amount of salts in solution is very considerable ; and the 
waters, being free from that fault of so many New Zealand springs, a large excess 
of silica, are fully equal to, and, indeed, in many respects surpass, the most celebrated 
of the alkahne waters of Europe. 

" In addition to the very large quantities of bicarbonate of sodium, the presence 
of considerable amounts of the chloride and sulphate gives these springs additional 
therapeutic properties of considerable value, and brings them into closer relationship 
with their European prototypes. Indeed, it is curious how many striking points 
of resemblance there are between the Te Aroha springs and those of a similar class 
in the Old World. At Vichy, Ems, Vals, and Royat — to take four famous examples — 
certain of the springs contain an appreciable quantity of bicarbonate of iron, with 
which is usually associated minute quantities of chloride of lithium ; and in the 
recently opened-up Spring No. 22 the same salts have been found in closely similar 
amounts. 

" It is probable that this trace of lithium may have some definite therapeutic 
properties, rendering the waters all the more suitable in gouty cases. The iron, though 
only present in small quantities, is yet in the easily assimilable form of ferrous 
bicarbonate ; and certain springs, such as Nos. 20 and 22, should be valuable in cases 
of ansemia associated with feeble digestion, in which the stronger iron waters are 
not well tolerated. 

" Though the waters are certainly not purgative in the ordinary sense of the word, 
yet the sodium-sulphate in solution tends to help their general laxative effect in certain 
individuals, and assists the action of the other salts, much in the manner of the 
' adjuvant ' of the classical prescription. 

" In addition to the thermal springs, there are two cold ones deserving of more 
than a passing mention ; these are No. 20, known as the '" Iron Spring," and No. 21, 
the " Magnesia Spring," both used for drinking purposes. No. 20 is a small spring of 
palatable water with a distinctly chalybeate taste. In addition to minute quantities of 
the same salts as are found in the hot springs, it contains about 12 gr. of magnesium, 
and 1-2 gr. ferrous bicarbonates per gallon, constituting an ideal water for mild cases 
of ansemia. The waters of No. 21 are cold, somewhat turbid, but very palatable, with 
a faint sweet after-taste resembling very weak lemonade. The amount of magnesia 
is somewhat greater, and of iron somewhat less, than in the case of Spring No. 20, 
while it constitutes a connecting-link between the latter and the thermal springs in 
containing a considerable amount of sodium-bicarbonate and a moderate quantity of 
the chloride. Such a water is invaluable in many cases of dyspepsia, especially when 
stronger waters are either not indicated or not well tolerated. The only drawback 
to the water is the somewhat high percentage of sihca present. 

" A few hundred yards from these springs, on private property, arises a group 
of cold springs of closely similar nature, but somewhat richer in magnesium aalta." 

* Joly, J. : " Radio-activity and Geology," 1909, p. 39. 

t WohJmann, A. S. : " The Mineral Waters and Health Resorts of New Zoixland," 191 1, p. (il. 



32 







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34 






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- ' * ' 






. 


Lithium-chloride 

Sodium-chloride 

Sodium-sulphate 

Sodium-bicarbonate 

Potassium-chloride 

Potassium-sulphate 

Magnesium-chloride 

Magnesium-sulphate 

Magnesium-bicarbonate 

Calcium-chloride 

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Ferrous bicarbonate 

Aluminium-sulphate 

Alumina 

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Silica 


00 

Is 

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* 


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0-9 
6-6 

0-2 
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41-5 

0-6 

7-8 


to 

CO 

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: : : : 


■c<ioob 'o ■ "^ ■ ' (k ■ 'o ■ t>- 








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2-5 

4-8 

0-1 

20-1 

24-0 

0-4 
5-5 


10 


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13 

00 • • 

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0-20 

8-1 

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2-2 
22-0 

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• 




Lithium-chloride 

Sodium-chloride . . 

Sodium-sulphate 

Sodium-bicarbonate 

Potassium-chloride 

Potassium-sulphate 

Magnesium-chloride 

Magnesium-sulphate 

Magnesium-bicarbonate 

Calcium-chloride 

Calcium-sulphate 

Calcium-bicarbonate 

Ferrous bicarbonate 

Aluminium-sulphate 

Alumina 

Sodium-silicate . . 

Silica . . 


to 


H 




^ ^ 

W W W 

13 13 13 13 
13 13 13 13 

tH k4 (4 Ch 

fe fe Eq pC( 



36 

All the springs are strongly effervescent, tlie gas given off consisting almost 
entirely of carbon-dioxide. Sulphuretted hydrogen, however, is present' to a greater 
extent than the analyses show. It may be detected in any of the cold springs, but 
does not seem to be so widely present in the warm. Three samples of gas given off 
by the cold springs were collected, and on analysis were found to contain the following 
gases :- 





B. 


H. 


K. 


Carbon-dioxide 


96-00 


95-21 


94-23 


Methane 


1-63 


1-66 


2-06 


Hydrogen 


Nil 


Nil 


0-49 


Oxygen 


Nil 


Nil 


Nil 


Nitrogen (by difference) 


2 -.37 


3-13 


3-22 



100-00 100-00 100-00 

No sample of the gas given off by the warm springs was collected. 



The Okauia Gtroup op Mineral Springs. 

Under this head is included a somewhat scattered group of springs which occur 
near the southern boundary of the subdivision. The principal springs of the group 
are just without the area examined. All these springs are obviously connected with 
a great fault which separates the mountains from the plain. The fault is here a step-fault 
consisting of three subparallel subsidiary faults, and hot springs occur in connection with 
each subfault. The most powerful springs are those in the ditch cut in the plain by 
the Waihou River. They are on the Une of the outermost subfault. Three of the 
springs are known as — Ramaroa, or the Opal Spring ; Paruparu, or the Ruby Spring ; 
■and Okohukura, which has a temperature of 117° Fahr. Ramaroa is a magnificent 
spring, with a temperature of 104° Fahr., and a flow of 28,000 gallons per day. 
This spring is but a few feet above the Waihou River ; and the limpid effervescent 
waters of the spring,, welhng with opaUne tints from a tuff bottom, pleasingly contrast 
with the sombre gray-green rapid current of the Waihou streaming close at hand. If 
there were not such a plethora of hot springs in this portion of the North Island, 
doubtless more attention would be bestowed upon this and the numerous other springs 
which rise in the bed and banks of the Waihou in this locahty. 

The following are analyses of water from the Ramaroa Spring : — 





Grains per Gallon. - 


Parts per 100,000. 




(1-) 


(2.) 


Sodium-chloride 


1-51 




Sodium-bicarbonate . . 


28-10 


44-7 


Potassium-chloride 


0-50 




Potassium-sulphate . . . . . . 


0-75 




Magnesium-chloride . . 




2-7 


Magnesium-bicarbonate 


4-44 


2-2 - 


Calcium-bicarbonate . . 


4-98 


8-7 


Ferrous bicarbonate . . 


0-08 




Alumina 


0-22 


0-5 


Sodium-silicate 




10-0 


Silica 


5-88 


-- 


Total solids 


46-46 


68-8 


Free carbon-dioxide . . 




5-5 


Temperature, Fahr. . . 


106° 


110° 



No. 1 analysis is taken from the 37th Annual Report of the Colonial Laboratory, page 16. 
No. 2, 45th Annual Report Dominion Laboratory, page 25. 



■;riTBj-da^g 



■qiiiBj-dG^g 



EH 



•^inL'j-da:^y 




H 

ta 

H 

K 



o 



CO 



as 



37 



There is also an incomplete analysis, relating probably to this spring, in the 15th Annual 
Report of the Colonial Laboratory, page 40, giving the total fixed salts as 21-04 gr. per gallon, 
and reporting a trace of sulphuretted hydrogen in the water. 

A partial analysis of the Paruparu Spring* was made in 1903 ; the result, expressed in 
radicles, is given below ; and for the sake of comparison the first analysis of the Ramaroa 
.Spring quoted above, also in radicles, is set beside it : — 



Grains psr Gallon 
(Ramaroa). 



Grains per Gallon 
(Paruparu). 



Soda 


8-01 




Potash 










0-70 




Lime 










1-68 


2-24 


Magnesia' 










1-20 


1-51 


Iron-oxide . . 










0-04 




Chlorine 










1-24 


1-33 


Sulphuric acid (SO3) . 










0-36 


. . 


Alumina 










0-22 




Silica 










5-88 


7-56 



It will be noted that as far as the analysis goes the Paruparu Spring closely resembles 
the Ramaroa Spring. 

The hot spring in the lower valley of the Waiteariki is in the Une of the central step-fault, 
and about 30 chains from the most eastern and main fault. Its temperature is about 
95° Fahr., and the surface is covered with a brownish frothy scum of algse. A sample of 

the water was collected, and on analysis gave the following result : — 

Parts per 100,000. 

Sodium-bicarbonate . . . . . . . . . . . . 21-1 

Magnesium-chloride . . . . . . . . . . . . 2-5 

Magnesium-bicarbonate . . . . . . . . . . 15-7 

Calcium-bicarbonate . . . . . . . . . . . . 26-6 

Ferrous bicarbonate . . . . . . . . . . . . 0-4 

Alumina . . . . . . . . . . . . . . 1-2 

Sodium-silicate . r . . . . . . 15-4 



Free carbon-dioxide 
Temperature, Fahr. 



82-9 
37-7 

95° 



The only other spring in the Okauia group is one rising from beneath the talus slope of 
the main fault-scarp. This is a tepid spring carrying so small an admixture of salts that it 
is used for domestic purposes by the Sheehan Bros. , upon whose farm the spring rises. It 
evidently varies somewhat in composition, for on rare occasions the water is unfit for cuUnary 
purposes. This spring, which has a flow of about 1 cubic foot per second, when its three points 
of issue are considered, is undoubtedly fed in large part by the mountain rills which lose them- 
selves in the upper portion of the talus slope. A sample of this spring was not collcctpd for 
analysis. 

Thk Waitoa Group of Mineral Springs. 

This group of springs and seepages is situated in the centre of the Hauraki Plain, about 
five miles east of Tahuna, and a like distance north-west of Waihou Railway-station. An 
area of low swampy land about 40 acres in extent, on both sides of the Waitoa River, contains 
a large number of springs, the temperatures of which range up to 170° Fahr. Only one 



* Colonial Laboratory: .'{"tli Annual Rcporl, 1001, ]>■ lt>. 



38 



sample was collected, from a spring having a temperature of 105" Fahr. This on analysis 
yielded the following result : — 

Parts per 100,000. 
Lithium-chloride . . . . . . . . . . . . 0-65 



Sodium-bicarbonate 
Sodium-borate 
Potassium-chloride . . 
Magnesium-chloride . . 
Magnesium-bicarbonate 
Calcium-bicarbonate 
Ferrous bicarbonate 
Alumina 
Sodium-sihcate 



Free carbon-dioxide 



60-9 
0-3 
5-06 
1-5 
4-6 

10-7 
0-3 
0-5 

20-6 

105-11 

284 



0-5 


1-1 


4-5 


3-7 


100 


10-6 


1-5 


1-5 



Springs which may be grouped with those just described occur near Walton, close 
to the southern limits of the subdivision. These were not visited, but according to the 
42nd Annual Report of the Dominion Laboratory they have a temperature of 83° Fahr., and 

contain the following salts : — 

Grains per Gallon. 
Sodium-chloride . . . . . . . . . . 1-7 2-0 

Magnesium-sulphate 
Sodium-carbonate . . 
Calcium-bicarbonate 
Sodium-sihcate 

18-2 18-9 

" The analyses show these to be faintly alkahne waters, but the alkahnity is very shght, 
and the amount of salts too small to allow the samples to be classed as mineral waters ; in 
fact, many city suppHes (London, &c.) contain much larger proportions of salts than are 
found in these waters."* 

On the drained area of the Piako Swamp the surface-waters contain so much organic 
matter as to render them unsuitable for human use, and numerous bores have been sunk in 
the hope of reaching an artesian supply. Water has been struck in all the bores, but in nearly 
every instance was so heavily charged with mineral salts as to render it unfit for domestic 
purposes. The writer had no opportunity of collecting a sample for analysis, but water 
collected from a bore near Keripehi,f about eight miles and a half north of the northern 
boundary of the subdivision, may be citedj as indicating the nature of this underground 
water : — 

Grains per Gallon. 
Alkahne chlorides . . . . . . . . . . . . 12-3 



Sodium-bicarbonate 
Calcium-carbonate 
Magnesium-carbonate 
Ferrous carbonate 
Sodium-sihcate 



43-4 
3-3 
2-9 

. 0-5 
9-7 



72-1 



* Dominion Laboratory : 42nd Annual Report, 1909, p. 31. 

t See Map 2 of this bulletin, and map of Waihou Survey District of Bulletin No. 10. 
j Dominion Laboratory : 42nd Annual Report, 1909, p. 36. Here the water is referred to a spring, but 
this is a mistake. (See Report of Department of Lands, 1907-8, p. 79.) 



39 



Katikati Group of Mineral Springs. 

Several subgroups of springs are here included. The springs of the most northerly sub- 
group rise for about 5 chains along the swampy bed of a small rill flowing into the Tuapiro 
Stream. A sample was taken from an excavation just beside the upper end of the swamp, 
and the water is no doubt contaminated by surface drainage. The temperature at the time 
the sample was collected was 93°, but varies according to local variations in rainfall and 

season. The sample contained : — 

Parts per 100,000. 
Sodium-chloride . . . . . . . . . . . . 1-72 



Sodium-bicarbonate . . 








. 540 


Potassium-chloride 


, 




, 


. 0-29 


Magnesium-bicarbonate 






, 


. 1-28 


Calcium-bicarbonate . . 








. 2-88 


Alumina and iron-oxide 






, 


. 140 


Sodium-sihcate 


• 




• 


. 6-59 



19-56 

Springs also occur close to the left bank of the Te Rere-atu-kahia Stream. Two excava- 
tions have been made, and Hned with concrete. The main spring wells up in the smaller 
excavation, while the larger, about 16 ft. square, receives the overflow from the smaller in 
addition to the flow of its own springs. The surface of both pools supports a greyish-green 
scum of algse, and a few luxury-loving eels were observed in the larger. Although river- water 
often carries a larger proportion of dissolved salts than these springs, and eels can hve in 
brackish water, this habitat is interesting from the fact that carbon-dioxide is constantly 
bubbhng from the floor of the excavation. The temperature of the water of both springs is 
about 97° Fahr. The water from the smaller excavation above the main spring was analysed 

with the following result : — • 

Parts per 100,000. 
Sodium-chloride . . ' . . . . . . . . . . 2-08 



Sodium-bicarbonate . . 
Potassium-chloride 
Magnesium-bicarbonate 
Calcium-bicarbonate . . 
Aluniina and iron-oxide 
Sodium-siUcate 



3-78 
0-29 
146 
4-86 
1-60 
8-05 

22-12 



Other springs which may be included in the Katikati group occur in the bed of 
the Te Puna Stream. These springs are cold, and rise at the foot of a rhyohte bank. 
As the stream flows directly over the springs no sample was collected. A warm spring 
is reported to occur below low-water mark in the estuary of the Te Puna. This was 
not observed. The water of which an analysis is given on p. 21, Colonial Laboratory, 37th 
Annual Report, may have been obtained from this spring. It is impossible to reconcile it 
with either of the analyses given above. 

Origin of the Mineral Springs. 

The origin of mineral springs has of late years been a much-vexed question, nor can it 
be said that finality has yet been reached. It wiU have been noted that at the beginning of 
the description of the springs an arbitrary classification was adopted. This was done because 
so far no satisfactory scientific classification has been devised. Two theories of spring-genesis 
are widely supported. 



40 

The older or meteoric theory is very simple, and is of universal application. It postulates 
that springs are but meteoric waters, which again reach the surface after a longer or shorter 
journey through the rocks. On this theory differences in composition of springs depend 
upon the journey the waters have made, and upon the nature of the rocks traversed. There 
is every gradation between spring- waters, which approach rain-water in purity, and waters 
which carry several per cent, of salts in solution. Long ago Bischof showed that such springs 
as rose upon mountain-slopes a considerable distance above the valleys carry but httle 
material in solution, while hot springs and carbonated springs in general, rose in valley- 
bottoms and at the foot of mountain-slopes.* He considered that the mineral-content of 
springs is leached from the rocks traversed by the water, and that the carbon-dioxide, so 
common in mineral springs is yielded by the silication of carbonates. Putting his con- 
clusion in a modern way, mineral springs are the overflow of the sea of underground 
water. 

The meteoric genesis of springs was not seriously questioned until 1902, when E. Suess,t 
in discussing the origin of the Carlsbad springs, revived an old theory, and advanced 
cogent reasons for believing that the waters of the Carlsbad springs arise from a deep- 
seated magma, and reach the surface for the first time. GregoryJ similarly considers 
that the springs and the waters of artesian bores of Central Australia are supplied by 
magmatic waters. 

Although the magmatic theory offers a plausible explanation of the vast quantities 
of common salt and carbon-dioxide brought to the surface of the earth by springs, and 
■ also of the constancy of temperature, flow, and mineral-content of many springs, never- 
theless the meteoric theory is so competent to explain the phenomena of carbonated 
springs, both hot and cold, that in the writer's opinion its applicability to any such 
spring should be rejected only after the closest inquiry and upon the strongest grounds. 
In' fact, the onus of proof is upon those who support the magmatic theory of spring- 
genesis for carbonated springs. 

It is not, however, proposed to discuss further the general question of spring-genesis, 
except in so far as the springs of the Hauraki Peninsula are concerned. As a prelimi- 
nary to this discussion the analyses of the springs of the Aroha Subdivision are 
tabulated on pages 42 and 43. The results are presented centesimally, after the ionic 
method recommended by Clarke,§ the only difference being that the carbonate ion 
is here represented as HCO3, whereas Clarke uses CO3. 

These tables show very clearly the difference in composition of the cold and warm 
springs of Te Aroha. In considering the cold springs, it will be noted that they vary 
considerably in composition, and this variation is the more remarkable when the 
contiguity of some of the springs is considered. Thus, springs B, C, D, and E arise 
in a space not more than 8 ft. by 12 ft., and the same may be said of F, H, and J. 
Again, analyses V, W, X, Y, and Z, executed in 1901, refer to the group of springs 
lettered A to K, but unfortunately cannot be referred to definite springs. Nevertheless, 
this very difficulty of reconciling the analyses with known springs points the fact 
that the composition of the waters of the cold springs is inconstant. Again, these 
springs are influenced by the rainfall, and their temperatures vary with the season of 
the year. No one would dream of contending that these cold springs were replenished 
otherwise than by waters of meteoric origin. 

The warm springs, on the other hand, closely resemble each other in the percentage 
composition of their salts. Springs 1 to 15 differ only in their degrees of salinity, 

* Bischof, G. : " Elements of Chemical and Physical Geology," translation, 1854, vol. i, p. 217. 
t Geographical Journal, vol. xx, 1902, pp. 517-22. Abstract of lecture by E. Suess. 
X Gregory, J. W. : " Flowing Wells of Central Australia." Geographical Journal, vol. xxxviii, 1911. 
§Clarke,"F. W. : " Data of Geochemistry," 2nd edition, 1911, p. 57. 



41 

while 17, 18, 21, and 22 may readily be accounted for by assuming an admixture with 
water similar in composition to some of the .difi'erent cold springs. Further, in respect 
to springs 8 and 15, the analyses of 1905 do not difi'er materially from those of 1889. 
It may be fairly assumed that all the warm springs are fed from a common source, 
which has maintained a constant composition over a period of at least sixteen years. 
This constant assemblage of salts may be termed the normal salts of the Te Aroha 
springs, and. the warm rising water uncontaminated with surface-waters may be termed 
the Te Aroha normal water. The total salinity of this normal water must be as 
great as the strongest of the springs — viz., No. 15, which has a salinity of 1,120 parts 
per 100,000. The temperatures of some of the springs — Nos. 1, 2, 4, and 6 — does not 
vary with the season, nor does the flow of any of the warm springs appear to be 
influenced by the amount of rainfall. No exact observations have, however, been made, 
and the total salinities of springs 8 and 15 differ considerably for the years 1889 and 
1905. 

The second analysis of the Ramaroa Spring quoted above was of water from the 
spring collected eight years after the first water analysed. The analyses agree well 
together, so their mean is probably very near the composition of the normal salts of 
the spring. 

In regard to the origin of the springs, it is known that the waters percolating 
from the surface are charged with oxygen and carbon-dioxide, two potent chemical 
agents. The oxygen is the more powerful : it oxidizes the sulphides present in the 
rocks, forming sulphates and free sulphuric acid, the latter of which attacks other 
constituents with production of sulphates. The carbon-dioxide attacks the feldspars of 
the rocks, rendering the alkalies readily soluble, and producing kaolin and silica. The 
potash is, however, liable to be recombined by the formation of potash-mica.* Now, 
as far as water-content is concerned, there are two zones of rock on the earth's crust — 
the upper non-saturated or vadose zone, and the lower saturated zone. The contour 
of the deep-circulation zone follows with softened outline the surface-contour, touching 
it along the surface drainage-lines. The non-saturated zone, or zone of weathering, lies 
between these two contours ; through it percolates all the water which reaches the 
saturated zone. The rocks of this vadose zone, then, are well leached by oxygenated 
and carbonated waters, and they, differ very considerably from their prototypes in the 
deep-circulation region. It has been shown by numerous writers that in andesites such 
as are here considered the feldspars are destroyed by weathering long before the ferro- 
magnesian minerals. The deeper region is much more extensive than the non-saturated 
zone, and according to Van Hisef may extend to a depth of 1 2,000 metres. The 
waters in this zone percolate through the capillary openings in the rocks, and graduall}' 
find their way to larger channels. When a large channel leading to the surface, siich 
as a great fault-zone, is reached, the waters may rise and escape as mineral springs 
chai'ged with dissolved salts and heated by contact with deeply buried rocks. Each 
trunk channel by which the waters ascend will have a fairly definite drainage-system, 
comparable to the basin of a river, from which to draw its supplies. The pi'incipal 
factor controlling the rate of flow is not precipitation, but the rate of percolation 
through the pores of the rock. When the amount of piecipitation is greater than 
the percolation-capacity of the rock the non-saturated zone fills up, any surplus 
precipitation joining the surface drainage. The now saturated zone of weathering 
acts as a reservoir, from which the deep circulation may draw su])plies until tiie 
next precipitation. 

* Van Hise, C R. : " IVeatise (Ml Metamorphism," 1904, p. 25(i. 
t Op. cit., pp. 160 and 104. 



42 






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44 

In regard to the drainage- system of tlie Te Aroha liot springs, the assumption may 
be made that the major portion is similar to the rocks of Te Aroha Mountain. This 
consists of andesitic breccias and flow rocks more or less propylitized. The spring- 
waters will naturally contain large amounts of the most soluble substances — i.e., the 
alkalies — and of these sodium will predominate over potassium, because the rocks 
contain more sodium than potassium, and because the potassium liberated from feldspars 
is liable to be fixed as sericite. The calcium of the waters is derived both from the 
feldspars and from the ferro-magnesian minerals, the small percentage of magnesium 
indicating the difficulty with which these are attacked. All the lime from the 
decomposition of the feldspars will probably not go into solution, as water, so long as 
sodium is available, will prefer the readily soluble carbonate of sodium to the difficultly 
soluble carbonate of calcium. The sulphate in the water is derived from the oxidation 
of the pyrite in the propylitized masses of rock. The chlorine is probably contained 
in the rain-water, and is derived from the neighbouring sea. Gray* found that at 
Lincoln, in Canterbury, 61-2 lb. of chlorine, per acre per annum was brought to the land 
by rain. Other observersf have proved the occurrence of chlorine in similar quantities 
for other coastal lands. Such an amount, if assumed for the Te Aroha Subdivision, is 
competent to account for all the chlorine contained in the Te Aroha waters. 

There remains the carbon-dioxide to account for. Three sources of supply are 
suggested : (1.) Carbon-dioxide liberated in the soil by the activities of living organisms. 
(2.) Carbon-dioxide produced by the action of acids upon carbonates in the rocks. 
(3.) Carbon-dioxide produced by the oxidation of carbonaceous material in the rocks. 

In regard to the amount of carbon-dioxide formed in the soil, the amount contained- 
in river-water affords a clue. Thus the English Thames at Kingston, where the water 
is pure, contains 30-3 c.c. per litrej or 5-98 parts per 100,000 by weight. The waters 
of a canal draining the Piako Swamp at Keripehi had the following composition§ : — 



Sodium and potassium chlorides 

Sodium-bicarbonate 

Calcium-carbonate 

Magnesium-carbonate 

Ferrous carbonate 

Sodiuni-silicate 



238-0 
The amount of the carbonates in this water shows how potent swamp-water laden 
with carbon-dioxide may become. 

In regard to the second source of carbon-dioxide und-erground, an obvious method 
of formation is from the production of sulphuric acid by the oxidation of sulphides. 
It is well known that all volcanic rocks carry sulphides as a primary constituent, and 
in propylitized areas the amount of disseminated sulphides may be very great. In 
such an area as the one from which the Te Aroha springs may reasonably be assumed 
to draw their supplies, the amount of sulphur contained in the rocks is competent to 
account for all the carbon-dioxide of the springs. The carbonates upon which the 
sulphates would act are contained in large quantities in propylitized rocks. The 
writer, however, does not consider that a large proportion of the carbon-dioxide in the 
Te Aroha springs is so produced, otherwise a very much larger proportion of sulphates 
would be expected in the waters than is actually contained therein. 





Gi 


•ainis per Gallon 




. 164-2 






. 41-6 






. 10-0 






. 16-6 


. . 




1-5 






4-1 



* Gray, G. : Trans. Aust. Ass. Adv. of Sci., vol. ii, p. 138. 
t See F. W. Clarke : " Data of Geochemistry," 1911, p. 50, for references, 
j Roscoe and Schorlemmer : " Treatise on Chemistry," 1897, vol. i, p. 315. 
§ Dominion Laboratory : 42nd Annual Report, 1909, p. 36. 



45 

The other acid concerned in the liberation of carbon-dioxide from carbonates is 
silicic acid.- It is well known that even cold water is capable of dissolving silica, and 
hot" water has a very much increased solvent-power. The silicic acid thus formed 
attacks the carbonates, with liberation of carbonic acid. This hypothesis was first put 
forward by Bischof,* and, provided an adequate supply of carbonates can be postulated, 
is a plausible explanation of the carbon-dioxide of springs. When applied to the springs 
of the Aroha Subdivision it explains why the Te Aroha springs, rising near a propyhtized 
area, carry such great quantities of carbonates, while the springs of Okauia, Waitoa, 
and Katikati, which have no areas of propyhtized rock to draw from, are not so heavily 
carbonated. 

The third method of producing carbon-dioxide, by the oxidation of carbonaceous 
matter contained in rocks, is apphcable to springs which rise through, or may be 
assumed to draw their supphes from, sedimentary beds. It may be assumed that the 
springs at Waitoa and Okauia have derived part of their supplies of carbon-dioxide 
from this source, seeing that these springs arise through recent subaqueous deposits 
which contain interbedded peat. 

Conclusion. 

Apart from the chemical composition of the contained salts, the springs of Ramaroa, 
Waiteariki, Te Aroha, and Puriri (some miles beyond the northern boundary of the 
Aroha Subdivision) are closely comparable, in that they all arise by way of fault-planes 
developed along the western base of the Cape Colville Range. The Puriri Spring, 
although similar to the hot springs of Te Aroha in chemical composition, resembles 
the cold ones in that it varies in flow with the rainfall, j and is therefore probably of 
meteoric origin. The spring arising near the Copland River, South Westland, has 
also been tabulated, in order to show how closely a spring remote from a volcanic 
district may resemble springs which many would consider of magmatic origin. It is 
apparent that the warm springs of the Aroha Subdivision, while differing greatly in 
composition among themselves, resemble other springs which almost certainly draw 
their waters from a meteoric source. As there is no difficulty in accounting for all 
the phenomena of the warm springs of the subdivision by deriving them from surface- 
waters, it is unnecessary to postulate a magmatic source for them. 

It is considered that all the springs of the Aroha Subdivision are supphed by 
waters of meteoric origin. The springs are the overflow of the sea of underground 
water ; and each group of springs, characterized by constant flow, temperature, and 
saline-content, represent the drainage from a particular basin of the underground water. 
There are two systems of springs at Te Aroha. The cold springs are of more superficial 
origin than the hot, and probably derive their waters from the zone of weathering. 
The waters of the hot springs at Te Aroha, on the other hand, are derived from a 
deeper and more extensive drainage-system, the waters of which have great masses of 
rock to leach, and the springs are thus able to maintain a constant flow, temperature, 
and saline-content for relatively long periods. 

* Bisohof, G. : " Elements of Chemical and Physical Geology," translation, 1854, vol. vii, p. 239 
t BtiUetin No. 15, IS 12, p. 33. 



46 



CHAPTER V. 



Introduction 

North-west Faults 

North-east Faults 

Other Faults 

The Thames Fault-complex 

The Miranda Fault-complex . . 

The Bay of Plenty Fault-complex 



FAULTS. 




Page 




Page 


. . 46 


Age of Faults 


.. 51 


. . 47 


Structure of the Aroha Subdivision 


.. 52 


. . 48 


Hangawera Earth-block 


52 


49 


Rift Valley 


.. 52 


. 49 


Cape Colville Earth-block . . 


. . 53 


. 51 


Coastal Plain 


54 


51 







Introduction. 

In the Aroha Subdivision, within the area covered by the Cape Colville Kange, 
the rocks are shattered by many faults. Volcanic accumulations offer pecuUar 
difficulties in the determination of the strike and dip of faults, especially when the 
sections available for examination are limited to creek-beds. Beyond the erosive 
activity of the streams, the moist, warm climate permits so strong a plant-growth 
that only in the most exposed positions, or where special circumstances intervene, do 
outcrops occur. The geologist has thus either to disregard altogether disconnected 
-crushed and sUckensided areas, or join them up in fault - zones, as his judgment 
directs. Such constructive work is by no means haphazard. It has been shown 
by many writers that faults tend to occur in parallel systems, and that one parallel 
system is generally crossed nearly at right angles by another similar system. Again, as 
W. M. Davis insists, maturity in topography brings an increasing adjustment of streams 
to structure. To this adjustment the main streams are less Hable than branch streams. 
Now, in such a district as the Aroha Subdivision, consisting of confusedly arranged 
beds of lava, breccia, and tuff, the only structural features hkely to have parallel 
orientation are faults and joints. The district has in general a submature topography, 
and the streams tend to produce a pattern nearly rectangular. 

W. H. Hobbs* writes : " No study of faults could be considered in any degree 
adequate which did not recognize that the faults proven to exist by the accepted 
methods can represent but a small fraction of their actual number. Unlike folds, 
which are open to inspection or to reconstruction whenever rocks outcrop at the 
surface, faults by their very nature tend to bury themselves from sight. . . . 

" It seems to have been rather generally overlooked that since geologists are 
required to color in their maps and prepare hypothetical sections where continuous 
outcrops are not present, as great violence may be done to the facts through the 
omission of faults which are probably present as by their introduction where they 
do not exist. . . . Theory and experiment are in agreement in indicating that 
faults, like joints and folds, seldom occur alone, but rather as elementary parts within 
series or systems." 

The work in the Aroha Subdivision has shown that the majority of the faults 
may be referred to two systems, which may conveniently be designated the north-west 
and north-east systems respectively. In the following descriptions the readily recognizable 
faults of each system will be first noticed. 



* Hobbs, W. H. : " Primary Fracture Pattern," Geological Society of America, vol. xxii, 1912, p. 165. 



47 

North-west Faults. 

The Waipupu Fault, so named because the Waipupu Stream follows along the 
course of this fault for some distance, shows for a distance of six miles shattered 
rock, friction - breccias, and intensely crushed pug - bands. Along its scarp the old 
Te Aroha - Katikati Track climbs, at a long angle, to the Rere-atu-kahia Saddle. This 
track had to be abandoned owing to the frequent shps of loose rock. The down- 
throw of this fault is here to the south-west, and amounts to at least 1,500 ft., this 
being the height of the top of the scarp above the plain. The strike is 130°, and 
if this direction be continued westward across the valley of the Waiorongomai the 
south-west face of Te Aroha Mountain is touched. There faulting, besides being 
indicated by the topography, is proved by the small hills of dacite breccia abutting 
against the solid andesite of the lower mountain. Where this line of fault reaches 
the plain occur the Te Aroha springs, which issue, as previously stated, from a mass 
of crushed rock at the base of a steep escarpment. 

The Minden Fault may be regarded as an eastern continuation of the Waipupu 
fracture. This fault strikes 120° along the north-east flank of Mount Minden. There 
is no stratigraphical evidence of its existence ; but the mineral springs of the Te Puna, 
and the lower series of waterfalls of the streams flowing northwards from the Whaka- 
marama Plateau, are sufi&ciently suggestive. 

Thompson's Track follows the abrupt south-westward-facing scarp of another 
fault belonging to this system. Along this track for a distance of eight miles there 
is no solid country ; andesites have been shattered to a jumble of angular blocks, 
and breccias crushed to a friable mass. The strike of this fault is about 130°, and 
if this line be continued south-east across the range a saddle between Ngatamahinerua 
and a subsidiary hill will be crossed. One of the head streams of the Kauritutahi 
drains from this saddle. The downthrow of this fault is to the south-west, and must be 
close on 2,000 ft. 

In proceeding north from the Waipupu Fault the first west-north-west fault . is 
the Wharawhara Fault, which follows the upper portion of that stream to its head. 
Crushed country occurs at numerous points along the valley of this stream. The 
disturbed rock in the valleys of the upper Waitawheta and the Waipapa may also 
be here correlated. The strike of this fault is about 126°, and the downthrow, judging 
from the topography, is to the south-west. 

In the northern portion of the subdivision it has been found impossible to connect 
with certainty the various crushed and shckensided areas with well-marked west- 
north-west striking zones. Such zones of faulting do exist, however, and the zones 
described below may be considered as probable. 

The great dyke crossing the Waitawheta River near Maungawhio-tapu Hill has a 
general west-north-west trend, and if its southern edge be continued eastward the 
disturbed- rock showing in the Wairoa and its branches will be reached. Again, if 
the northern edge of the big dyke (greatly obscured by overflow) be continued eastward 
the gorge of the Tuapiro is found to be in line. No crushing is to be observed 
here, but the country on the south side of the river is andesite breccia, while on 
the north it is younger rhyohte tuff. The south wall of the great dyke is well 
exposed where the Waitawheta has cut a gorge through it, and here has a strike 
of 114° (meridian). This corresponds with the general strike of the proved west- 
north-west faults of the district. 

The large dykes exposed in the Wairoa and the Waiau streams, and the one 
which limits the Waihi Plain on the south from the Mangakiri to the Waimata, have 
similar strikes. With this last-mentioned dyke may be correlated the numerous crushed 
and shckensided areas exposed in the middle course of the Waiau Stream. 



48 

Mining operations at Karangahake have proved the existence of numerous faults. 
These faults, which are all of a minor nature, have an average strike of about 112°, and 
any one of them departs but a few degrees from this direction. The fault which crosses 
the Rahru Saddle, and crushes the carbonaceous beds exposed in the Ohinemuri Valley 
about 18 chains above the eastern end of the railway-tunnel, also belongs to this group. 

About 60 chains to the north of the big Waitawheta dyke is an outcrop of 
crushed mudstone, which may be correlated with a similar area in Romunga Creek. 
A low saddle connects these two points, and the strike from the one to the other is 118°. 

North-east F.a.ults. 

Following the system adopted in connection with the west-north-west striking 
faults, and commencing with those faults the strike and individuahty of which are 
obvious, the Waiharakeke-Waitakohe Fault will be first described. 

This great fracture crosses the Cape Colville Range from one side to the other. 
Along it the Waitakohe and Waiharakeke have cut their valleys. The low saddle 
between is crossed by Thompson's Track. The north-west face of Ngatamahinerua 
is the scarp of this fault, which here throws to the north-west. Crushed and shcken- 
sided rock is abundant in both creeks. The general strike of the fault is 44°. 

South of this fault a similar fracture crosses the mountain-ridge by the col 
between Ngatamahinerua and Pukepenga peaks. The strike is about 45°. In the 
Maungapukatea abundant direct evidence of faulting is available, but in the Kauritutahi 
the evidence is topographical. 

Similarly in the south branch of the Kauritutahi the long straight course of this 
stream suggests faulting, though there is no direct evidence. The general bearing of 
this stream is 23°. 

Still farther south the Puketutu Stream occupies a profound caiion with vertical 
walls. For more than half the length of this canon the andesites show at the base 
of the breccias on the north-west side of the stream, while only breccia outcrops on 
the south-east side. The straightness of the canon and the depth the stream has 
cut into the Okauia Fault scarp, when compared with the small notches that the 
much larger Wairere and Waiteariki streams have cut, also demand an agency other 
than stream erosion to explain its formation. The strike of this fault is 68°, and 
the downthrow, which is not great, is to the south-east. 

Between the Puketutu and Maungapukatea streams the Parengorengo has cut a 
deep gorge along a fault-hne which strikes almost exactly east and west. This fault, 
like the Puketutu Fault, crosses the range between Pukepenga and Te Ariariparitapu 
mountain-peaks . 

For a considerable distance north of the Waiharakeke-Waitakohe Fault there are 
no zones of broken country which can be referred to the north-east fault-system. 
Here the stress which produced the north-east system of' faults seems to have been 
relieved by an extensive sheeting of the country. The succession of beds in this 
locality fortunately permits of some of the sheeting-movements being recognized. A 
dacitic series of lavas and pyroclastics overlies flow andesites, which contain occasional 
irregular bands of breccia interbedded. In the left branch of the Te Rere-atu-kahia 
Stream three vertical junctions between the dacitic and andesitic series may be observed. 
The Wharawhara and the upper Waitawheta cross the sheet-fractures at various 
angles, but the exposures and succession here are not suitable for the observation 
of such minor structures. It is believed that these fractures have controlled the 
courses of the branches of the Waipupu, Wairakau, and Pohomihi, also that of the 
upper Waitawheta and the south branch of the Te Rere-atu-kahia. The peculiar 



Plate VT. 




llocK Plate at Hioad op Wahine Creek. 




Knohr of JIock at Head ov Waii'upu, siiowiNf! Waii-lit Pond in ForiEnno 



IND. 



Geo. null. No. 7(1.] 



\ To fare -p. f/S. 



49 

isolated plates of rock which stand out like wedges at the head of the Wairakau, 
and to a less extent at the head of the Te Eere-atu-kahia, and also the subequally 
spaced knobs of rock at the head of the Waipupu, are believed to be topographical 
expressions of thii5 sheeting. The lode fissures of Te Aroha indicate the existence 
of a sheeted zone in that locality. The fissures at Karangahake, although in this 
area a north-striking set of fissures complicates matters, may be similarly interpreted. 
The orientation of the majority of the lode fissures at Te Aroha and Karangahake is 
parallel to the fissures of the sheeted country farther south, and a fair inference is that 
the same stress produced them all, and that they are approximately of the same age. 

The stress producing this sheeting has at various places found relief in powerful 
faults. Thus the south head branch of the Te Eere-atu-kahia follows a fault-Kne 
which, produced north, separates the lowlands from the volcanic rocks of the range. 
Parallel to this a fault follows the lower portion of the gorge of the Waiau, and 
crosses the Hikurangi Eidge a little to the east of the summit. 

Near Karangahake occur the Waitoki-Orima and Eomani faults. The former 
strikes north-east along the valleys of the Waitoki and Orima streams, and again 
manifests itself in the Ohinemuri ' Valley a little below Owharoa. The strike is 38° 
and the downthrow to the south-east. 

The Eomani Fault follows the course of the Eomani Stream. In the valley of the 
Eotokohu, along the north-west scarp of Karangahake Mountain, much crushing occurs. 
Crushing may also be noted on the Eotokohu side of the saddle jsetween Karangahake 
and the Eotokohu basin. Along the road leading from this saddle to Karangahake 
Township crushing is very manifest. The crush-zone a little above the Crown battery 
belongs to this fault. 

Other Faults. 

There is some evidence that another system of faults, with a strike nearly north 
and south, traverses the Aroha Subdivision. To this system belongs the Okauia Fault, 
which is the best-marked physiographically of any fault within the subdivision. 
This fault separates the Whakamarama Plateau from the Hauraki Plain. Within the 
subdivision it has a length of at least seven miles, and apparently extends several 
miles to the southward of Okauia. Crushing, which may be referred to this fault, is 
shown in every stream crossing it with sufficient volume to cut down its own shingle- 
fan and the talus of the fault-cUff. The Maungapukatea, Parengorengo, Puketutu, 
Wairere, and Waiteariki are such streams. At Okauia, near the southern boundary 
of the subdivision, step-faulting in connection with this fault is well shown. There 
are three step-faults, and hot springs occur in the hne of each one. The strike of 
the fault as a whole is about 165°. The downthrow is to the west, and varies from 
1,500 ft. to 2,500 ft. 

The zone of siUcification, known as the Waiorongomai Biick Eeef, is beheved to 
be a crush-zone. It may be traced almosf; continuously for a distance of almost 
three miles. It is not unhkely that the course of the Mangakino has been determined 
by the northward extension of this fracture. The strike of the known siHcified zone 
is about 185°. 

Parallel to the Buck Eeef, and about 40 chains from it, is another large fault- 
zone. It is along this crushed zone that the Waiorongomai has cut its deep gorge. 

The Thames Fault-complex. 

The remarkable western scarp of the Cape Colville Eange attracted the attention 
of the earUest observers. Thus Dieffenbach in 1841 says, " Throughout their extent 
4 — Aroha. 



50 

these mountains are abruptly separated from tlie plain, and, in fact, bound it like 
an artificial wall."* 

Hochstetter, viewing the plain and the Cape Colville Range from Pirongia Mountain, 
says, " It is only the steep margin, of the eastern coast range frojji Paterere Plateau 
to Aroha Mountain that forms the eastern boundary of the basin [i.e., the plains of the 
Waipa, Waikato, Piako, and Waihou]. This whole basin was, previ'ous to the last elevation 
of North Island, which was probably connected with the volcanic eruptions in the 
centre of the island, a bay of the sea, extending from Hauraki Gulf far into the 
interior. The steep margin of the surrounding ranges has continued to this day 
displaying the seashore of old ; and the singular terrace-formation on the dechvities of 
the hills and the river-banks ■within this basin is the result of a slow and periodic 
upheaving. "■[■ And again, speaking of the country near the Wairere, he describes the 
Whanga Plateau as " breaking off abruptly towards the plains of the Waiho and Piako." 

Although Cox J described the Moanataiari Fault and Beach Shde as early as 1882, 
and Park§ the Collarbone Fault in 1894, it was not until 1905 that the pecuhar 
topography of the western edge of the Cape Colville Range was referred to faulting on 
the large scale. In that year Lindgren|| pointed out that the Hauraki Plain probably 
occupied a grcihen, valley, and that the western face of the range was a fault-scarp. 
This view of the formation of the plains and the range has been indorsed by Morgan,^ 
Fraser,** and Maclaren.ff 

W. M. Davis, in speaking of block mountains in general, says, J J " The simple 
continuity of the base-line, and the complete absence of rock-outcrops on one side of 
it, are essential consequences of long-continued block-faulting, and are at the same 
time not characteristic of any other available geological process." These characteristics 
apply to the western face of the Cape Colville Range. 

The strike of this great fault-zone from the southern Umit of the Aroha Subdivision 
to the eastern shore of Hauraki GuH is, disregarding minor irregularities, approxi- 
mately 340°. Within the subdivision the faults have been divided into two chief 
systems, with strikes of about 40° and 120° respectively. At Thames, the only other 
locahty where individual members of the complex have been studied, the strike of the 
Beach SHde and Moanataiari Fault, as mapped by Fraser, is about 125°. These 
faults, together with the Collarbone Fault, are considered by Fraser to be subsidiary 
fractures of the Thames complex. It is suggested that the stress which produced 
the complex was superimposed upon an area already shattered by systems of faults, 
and that, wherever possible, rehef was obtained along pre-existing fissures. Thus the 
face of the range presents to the Hauraki Plain a series of sahents and re-entrants, 
the re-entrants filled with masses of faulted and jumbled country. 

It has already been noted that the streams show progressively maturer valleys 
as the range is followed north from Okauia. This change takes place in stages. 
Thus from Okauia to Ngatamahinerua the streams are exceedingly youthful ; the Waite- 
ariki and Wairere reach the plain by small notches cut on the edge of the fault-scarp, 
while the Puketutu, Parengorengo, and Maungapukatea, though entering at grade along 
fault-hnes, receive their tributaries over rapids and falls. Between Ngatamahinerua and 



* Dieffenbach, Ernest : " Travels in New Zealand," 1843, vol. i, p. 413. 
t Von Hochstetter, Ferdinand : " New Zealand," 1867, p. 306. 
} Cox, S. H. : Geological Reports, vol. xv 1883, p. 12. 

§ Park, J. : " Geology, Resources and Future Prospects of the Thames Goldfield," Mines Reports, 1894. 
C.-3, p. 59. 

II Lindgren, Waldemar : Engineering and Mininq Journal (New York), vol. Ixxix, 1905, p. 218. 

^Morgan, P. G. : Of. cit., p. 861. 

** Fraser, Colin : Bulletin No. 10, p. 16. 

ft Maolaren, J. M. : " Gold," 1908, p. 309. 

IJ Davis, W. M. : " Physiographical Essays," 1909, p. 734. 



51 

Te Aroha mountains the streams are somewhat more mature, while northward from 
Te Aroha the streams have submature valleys. This submature stage is apparently 
continued to Thames, beyond which point the writer cannot claim a personal knowledge. 
These differences in the sculpturing of the fault-scarp imply that different portions 
of the scarp are not all of the same age — ^in fact, that faulting progressed from the 
north southward. This supposition is supported by the abundance of hot springs from 
Te Aroha southward, as at Okauia, Okoroire, and Tirau. Moreover, direct evidence of 
faulting along the edge of the hills is wanting north of Te Aroha, although abundant 
south of that town. 

Miranda Fault-complex. 

The facts that a fault exists along the western scarp of the Cape Colville Range 
and that the Hauraki Plain is down-faulted are of themselves sufficient to suggest 
that a fault will be found near the western margin of the plain. Within the Aroha 
Subdivision no direct evidence of such a fault can be found. There the plain imbricates 
into the low hills in a most compUcated manner. Nevertheless, if a Une be drawn 
tangent to the eastern tips of the spurs of the Hangawera Hills^ its continuation 
northward will trace the boundary between the Pataroa Range and the plain and 
gulf farther north. The writer has not had an opportunity of examining the abrupt 
eastern scarp of the Pataroa Range, but near Miranda hot springs occur, and it seems 
reasonable to conclude that a fault, as indicated by Lindgren, hmits the Hauraki 
depression on the western as well as on the eastern side. This fault may be termed 
the Miranda Fault. It is probably a fault-complex similar to the Thames Fault- 
complex. 

Bay op Plenty Fault-complex. 

The Cape Colville Range presents to the Bay of Plenty an abrupt face, although 
not so abrupt as that shown by parts of the western scarp. North of the subdivision 
this, the eastern scarp of the range, has been steepened by marine erosion, and cUffs 
some hundreds of feet in height border the coast. 

Within the subdivision several of the minor scarps of the range may be referred to 
an extension of known faults. Thus the Hikurangi Fault may be continued along 
the range-front for some distance north of the Waiau. Similar extensions in respect to 
the Rere-atu-kahia, and Waiharakeke-Waitakohe, and Thompson's Track faults may 
also be made. In the writer's opinion, the inference that the Cape Colville Range is 
bounded by an eastern fault-complex, which may be termed the Bay of Plenty Fault- 
complex, is justifiable. 

Age op the Faults. 

Concerning the age of the faults but little can be said with certainty. It is 
assumed that each system of subparallel faults was caused by separate stresses, and that 
all the faults of each system were initiated at about the same time. The next chapter is 
devoted to a discussion of the geology of the district, and the classification adopted 
may be here reproduced in order that the reader may the more easily follow the 
statements made. The succession of volcanic rocks, commencing with the youngest, 
is as follows : — 

Dyke Series. 

I Younger. 
■• (Older. 

I Breccias and tuft's. 
Mudstoues. 
Flow and crystal tuft's. 
Andesite Series . . . . . , . . Flow and fragmental. 

4* — Aroha. 



Rhyolite Series 



52 

The youngest faults are tliose whicli strike west-north-westward. The stress 
which produced these also found relief by the intrusion of the dykes of the Dyke 
Series. They are thiis younger than all the members of the Rhyolite Series. 

The north-east striking faults are next in age. The lode fissures of the Karanga- 
hake and Te Aroha mining-areas belong to this system ; ^and these, as far as has been 
observed, penetrate only the Andesite Series and the lowest member of the Dacite 
Series. 

Again, the great Buck Reef of Waiorongomai, which is correlated with the 
north-striking fractures, is older than the north-east striking lodes of that area. 

Other considerations support the relative ages here given, such as the comparative 
prominence of the three fault-systems, but the writer does not regard the evidence 
upon which the statements of the ages of the fault-systems are based as entirely 
conclusive. Probably also each earth-movement which has affected the subdivision 
since the extrusion of the volcanic rocks has renewed the activity of some at least of 
the faults of each system. 

Structure of the Aroha Subdivision. 

It is abundantly clear that none of the Tertiary rocks outcropping within the 
limits of the Aroha Subdivision have steep dips persistent over considerable areas. 
Steep dips are not infrequent, but in every case may be referred to faulting. The 
earth-movements which have disturbed the subdivision during Late Tertiary and Recent 
times have not produced folding, and the available evidence seems to show that all 
the movements have been of the plateau-forming order. The writer beUeves that 
the Aroha Subdivision is divided into four major earth-blocks or provinces by the 
three fault-complexes already described. These, in order from west to east, may 
be designated — (1) Hangawera Earth-block, or G-rauwacke Province ; (2) Haurald 
Plain and Gulf, or Rift Valley; (3) Cape Colville Earth-block, or Volcanic Province; 
(4) Coastal plain. 

The study of faults in other countries has shown that " they may pass into folds 
either vertically or horizontally."* Of the earth -blocks Just mentioned, the Hangawera 
and Cape Colville blocks are elevated relatively to the other two. It is therefore possible 
that the Hangawera Hills and Cape Colville Range consist of earth-bocks resting 
upon the crests of great antichnes, into which the strata beneath, at present in the 
zone of flow, are folded. The longitudinal extent of the earth-blocks supports this view. 

Hangawera Earth-block. 

Since only the small portion of the Hangawera Block lying within the subdivision 
was examined very httle can be said concerning this earth-block. It consists of 
steeply dipping grauwackes and argilUtes, and is a portion of the fundamental mass of 
the North Island. Small patches of andesitic rock occur here and there over the 
surface of the older sedimentaries. The longitudinal extension of the block is meridional, 
and it stretches northward as the Pateroa Range beyond the hmits of the Aroha 
Subdivision. 

Rift Valley. 

This great depression hes between the Hangawera and Cape Colville earth-blocks. 
It has a width of about ten miles within the area examined, and is here filled Avith 
Recent Httoral and fluviatile deposits. Farther north it forms the Hauraki Gulf. 



* Chamberlin and Salisbury : " Geology," 1904, vol. i, p. 491. 



53 

Gape Colville Earth-Uock. 

Strictly speaking, tlae Cape Colville Eange must be considered to end in the 
Ngatamahinerua Ridge. As Hochstetter long ago pointed out, the Whakamarama 
or Whanga Plateau must be regarded as part of the Paterere Plateau, which stretches 
to Rotorua.* The south-eastern portion of the Tauranga Survey District includes a 
portion of this Paterere Plateau, and Maunganui Mount was also at one time part 
of the same plateau. f For the purposes of this section, the Whakamarama Plateau 
will be considered as part of the Cape Colville Range. The following paragraphs 
are largely of a speculative nature, and probably a study of the range, more detailed 
than the writer was able to attempt, would render nugatory many of the conclusions 
set forth. 

The principal faults which traverse the range within the subdivision have already 
been described, and the position is taken that if the range owes its formation to an 
adjustment of earth-blocks to different relative heights, then the smaller earth-blocks 
of which the range itself is composed are also hkely to be differentially elevated. 
Both the stratigraphy and topography support this view. The writer is well aware 
of the weakness of stratigraphical evidence as appUed to the correlation of volcanic 
beds such as here make up the whole of the Cape Colville Range, and in the following 
paragraphs relies mainly upon topographical evidence. 

That portion of the Cape Colville Range which Hes within the subdivision may 
be divided into several earth-blocks, which, though traversed by many faults, have 
yet preserved their identity through the last tectonic movement, and may thus in this 
discussion be regarded as unit blocks. 

The most northerly of these may be termed the Waitawheta Block. This block is 
roughly lozenge-shaped. It is bounded on all sides by faults, or rather fault groups, 
of which only representative members need be named — viz., the Waipupu, Waitakohe, 
Waiau, and Waitold-Orima faults. Distributive step-faulting along the periphery of 
the block, combined with subsequent denudation, has rounded the edges to a greater 
or less degree. From a point of vantage — say, Karangahake Mountain — the gradual 
rise of the ridges from the Waihi Plain to Te Aroha and Ngatukituki mountains 
may be noted ; and if the irregularities of the foreground be ignored, and the general 
slope of the country be considered, it is easy to conceive of the present drainage- 
system having been carved from an inchned plane which sloped from Ngatukituki and 
Te Aroha to the Waihi Plain. This old inchned plane, of which the present ridges are 
the traces, is considered to have been the mature base-levelled plain of the ancient 
Ohinemuri. On a previous page it has been stated that the drainage-system of the 
old Ohinemuri had, during the last elevatory movement, been tilted eastward, and 
that as a consequence the river had lost a large branch which had once flowed 
into it from the south near the eastern border of the ancient basin. The grade of 
the Waitawheta and the Mangakino is more gradual than the crest slopes from Ngatuki- 
tuki to the Waihi Plain. Now, the present drainage-system is submature, while the 
available evidence indicates that the old Ohinemuri basin had reached a mature stage 
of erosion. From these facts it may be inferred that during elevation the surface 
of the earth-block was tilted from the south northward. The actual slope of the 
tilted surface is apparently north-north-east. This is the slope of the plateau-hke 
country at the head, of the Waitawheta and the branches of the Tuapiro. 

Another unit earth-block forms the Whakamarama Plateau in the south of the 
subdivision. It also is roughly lozeuge-shaped. The Okauia, Puketutu, and Mindeu 
faults form its boundaries within the subdivision. The dissection of the surface of 



♦ Hochstetter, i'\ vou : " New Zealand," 1867, p. 446. f Op. cU., p. 441. 



54 

this earth-block has not proceeded very far. This impHes a recent elevation. The 
tilt of the block is evidently to the north-east, and the south branch of the Aongatete. 
the Whatakao, the Wainui, the Waipapa, and the Te Puna are consequent streams 
draining its surface. The Wairere and the Waiteariki, as well as the Ruangarara and 
the other branches of the Wairoa River, are streams which have pirated parts of 
the basins of the first-mentioned group of streams, and which owe their success to 
the greater elevation of the edges of the earth -block over which they flow. 

Immediately to the north of the Whakamarama Plateau rises a long narrow 
ridge, of which Ngatamahinerua is the most northerly and highest point. This may be 
<;onsidered a unit earth-block. The breccias which cap the ridge dip to the south-east. 

The Coastal Plain. 

The physiography of the coastal plain has already been described under the headings of 
the Katikati Lowlands and shore-Une. The silts and sands which form it are beheved 
to be but the superficial mantle of a foundered earth-block. According to this view, 
the rhyolite-outcrops of Te Ho and Te Karewa, and the andesite-outcrop on Mata- 
kana Island, are the only visible remnants of a province similar in structure and Uthology 
to the volcanic province which forms the Cape Colville Range. This foundered earth-block 
is the " island shelf " of Bell and Fraser.* Its width is unknown, as is the distance 
it extends to the north. It must end to the south against the Paterere Plateau, 
either within or close to the Aroha Subdivision, but the field-work undertaken in this 
portion of the subdivision was insufficient to permit of a discussion as to the manner 
of its ending. 

* BeU, J. M., and Eraser, C. : BuUetin No. 15, 1912, p. 31. 



9 
^ SEA LEVEL 




a. Recent. h. Volcanic. t. Older sedimentary. 

DiAGfiAMMATIC SECTION ACROSS HaUEAKI PenINSVLA. 



55 



CHAPTER VI. 



GENERAL GEOLOGY. 



Preliminary Statement 
Views of Other Writers 
Tlie Trias-Jura Series 
The Andesite Series . . 

Distribution 

Succession 

Petrology 

Age and Correlation 
The Dacite Series 

Distribution 

Succession 

Petrology 

Age and Correlation 
The Rhyolite Series . . ' 

Distribution 

Succession 

Petrology of Older Rhyolites 

Petrology of Younger Rhyolites 

Age and Correlation 



Page 
56 
57 
57 
58 
58 
59 
59 
63 
63 
63 
64 
65 
67 
68 
68 
68 
69 
70 
73 



The Dyke Series . . . . . . 73 

Distribution . . . . . . 73 

Petrology . . . . . . . . 74 

Age and Correlation . . . . 75 

The Tauranga Series . . . . . . 75 

Distribution . . . . . . 75 

Succession . . . . . . 76 

Age and Correlation . , . . 77 

Recent Deposits . . . . . . 77 

The Hauraki Petrographical Province . . 78 

Cause of Volcanic Eruptions . . . . 80 

Extent and Nature of the Andesite Ac- 
cumulations . . . . . . 81 

Period of Propylitization . . . . 81 

Correlation of the Rhyolites and Post- 

Rhyolitic Dykes . / . . . . 82 

Geological History . . . . . . 82 



Preliminary Statement. 

From the previous chapter it will have been gathered that the writer beheves the 
subdivision covers portions of four earth-blocks, two of which are elevated and two 
depressed. The oldest rocks of the district are exposed in the most westerly of 
these blocks — the Hangawera Block. In the Hangawera Hills are argillites and 
grauwackes which probably belong to the great Mesozoic formation of this portion 
of the North Island. They are overlain by breccias and flow rocks of an andesitic 
facies. The mature topography obtaining in the Hangawera Hills is not favourable 
for geological observations, and no contact between the two formations was discovered. 

The elevated earth -block forming the Cape Colville Eange is much more comphcated 
in structure than the Hangawera Earth-block. Within the subdivision it is formed 
of rocks of volcanic origin, and of such sedimentary beds as are likely to form between 
the pauses of volcanic activity. Its basal portion, however, consists, hke the Hanga-j 
wera Block, of argilUtes and grauwackes. These are well exposed in the northern 
portion of the Hauraki Peninsula,* and isolated exposures occur as far south as 
Thames,f but within the boundaries of the Aroha Subdivision no exposure in situ is 
known save that already mentioned in the preceding paragraph. Several years ago 
Professor Park,J in crossing the range south of Te Aroha by the Tuahu Track, noted 
a small outcrop of argilhte, but although the present writer made dihgent search in 
the locality he was unable to discover it. The outcrop must be quite inextensive, 
and is now probably covered by vegetation. Again, it has been reported that argilUtes 
were reached in a borehole sunk by the Woodstock Company to a depth of 1,100 ft. 
below sea-level. The writer could not obtain verification of this, but regards it as 
exceedingly probable, as a breccia carrying fragments of argillite and grauwacke 
forms part of the country in the TaUsman Mine. It seems certain that the Mesozoic 
rocks occur beneath the volcanics of the southern portion of the Cape Colville Range, 
and the writer believes that they are not buried more than 1,000 ft. below sea-level. 



* Fra.scr and Adams : UuUetin No. 4, pp. 40-52. 
t In letter, 20th July, 1910, to C Fraser. 



t I'^raser, C. : Bulletin No. 10. pp. 20-22. 



56 

The oldest volcanics exposed within the subdivision are andesitic rocks. These 
consist chiefly of lava-flows ; breccias form less than 20 per cent, of the mass of these 
rocks. The rocks represented among the various flows may be divided into horn- 
blende and pyroxene andesites. Again, these diiJerent classes of andesites are referable 
to several types. Thus among the hornblende andesites occur hornblende andesites. 
quartz - hornblende andesites, enstatite - hornblende andesites, hypersthene - hornblende 
•andesites, and augite-hornblende andesites ; while the pyroxene andesites are represented 
by augite andesite, hypersthene-augite andesite, and hypersthene andesite. Intermediate 
types between the hornblende and pyroxene andesites are also found. The lodes of 
the subdivision occur chiefly in the propyhtized faeies of the pyroxene andesites ; never- 
theless, the writer beheves that the hornblende andesites are, as a whole, older than 
the pyroxene andesites. The reasons determining this wiU be set forth later. 

After the extrusion of the andesites a pause in the extreme phases of vulcanism 
permitted the growth of vegetation, and in places the accumulation of subaqueous 
beds. The next series of volcanic rocks are dacitic in composition. There is httle 
agreement among petrologists as to the rocks to be included under the term " dacite." 
Some make the term include andesites which contain quartz phenocrysts ; others restrict 
it to rocks intermediate in composition between true andesites and rhyoHtes, and in 
this report the term " dacite " refers only to such rocks. The lowest member of 
the series is a glassy dacite, which sometimes shows a development of spheruhteF. It 
is followed by a crystal tuff, which may grade into a breccia. The dacite-flows and 
crystal tuffs are very closely connected, and are often in distinguishable in the fleld. 
The crystal tuffs are followed, apparently conformably, by volcanic ash and sand beds, 
which usually contain sufficient andesite and dacite fragments to justify their being 
called breccias. There is probably some unconformity between the crystal tuffs and 
the sandy breccias, as in the middle basin of the Waitawheta mudstones carrying 
carbonaceous bands near their base are intercalated. 

Overlying the formations already mentioned, and to a great extent filhng in old 
denudation valleys, is a series of rhyohtic pumiceous tuffs overlain by spheruhtic 
rhyolite. Younger still than these spheruhtic rhyohtes, but nowhere affording clear 
contacts with them, is a series of pecuhar tuffs — the so-called " wilsonite " — broken 
through and overlain by a Hthoidal rhyohte. Probably connected with the wilsonite 
tuffs are beds of subaqueous tufaceous material, which form in part the Katikati 
Lowlands. 

Quiescence in vulcanism and denudation probably on an extensive scale followed. 
Within the subdivision volcanic activity next manifested itself by the intrusion of 
numerous dykes. The largest of these, which may be termed the Waitawheta dyke, 
has a surface flow in close connection with it. No breccias are referable to this 
eruption. 

Overlying the Katikati beds are a series of gravels, sands, and clays, apparently 
of deltaic deposition, which in places carry thick seams of hgnite. Correlated with 
these are the sand and clay beds which form the downs near Walton, and have a 
considerable development towards Cambridge, in the Waikato district. 

The pumice sands of the Hauraki Plain are younger than the material forming 
the downs near Walton. Pumice sands also overlie the Tauranga beds at the southern 
end of Tauranga Harbour. 

The youngest deposits in the subdivision are the gravels and sands of the flood- 
plains of the streams, the swamp deposits of the Hauraki Plain and Katikati Lowlands, 
the sand-dunes of Matakana Island and other portions of the coastal belt, and the 
mud-flats and sand-banks of Tauranga Harbour. 



TABLE OF GEOLOGICAL FORMATIONS COMPARED WITH THOSE OF PREVIOUS WRITERS. 



HOOHSTETTER, 1867. 


COX, 1882, 


McKAY, 1905. 


Present Bulletin. 


Bulletin No. 4, 1907; Bulletin No. 10, 1910; 
Bulletin No. 15, 1912. 


PARK, 1910. 


Eecent and Post-Tehtiary. 




Recent and Post-Pliooenb— 
Beach-gravels. 


Recent and Pleistocene — 

(1.) Pumice deposits, river, swamp, and 

talus deposits, sand-dunes, and 

harbour muds. 
(2.) Raised beaches, high-level terraces, 

and Piako beds. 
(3.) Tauranga beds. 


Recent, Pleistocene, and Pbb-PLeistocene— 
Unconsolidated or poorly consolidated debris ; 
river-terraces, river-flats, drifting sands, talus 
slopes, harbour muds, and swamp deposits. 


Recent and Pleistocene. 




Included with Other Series. 


Post-Rhyolitic Dykes. 


Dyke Series. 


Intrusive Igneous Rocks op Various Periods. 


Not Specially Mentioned. 




Pliocene-- 

Rhyolite formation. 


Pliocene — 

(1.) Younger rhyolites. 


Rhyolite Series— 
Younger Rhyolites {^';^-^^^^^j^ 


Pleocbnb — 
Tertiary Volcanic Rocks op the "Third 
Period "— 
Acidic iJ^Rhyolitio tuffs, breccias, and lava- 
flows. 






(2.) Middle rhyolites. Flow. 


fElow. 
Older Rhyolites 






(3.)- 


^Breccias, chiefly acidic. 


' Pragmental. 


Newer Pliocene — 
Rhyolites. 




^Pumiceous sand with lignite. 


Dacite Series — 

(1.) 'Pragmental with dacite and ande- 
site fragments. 


Tbbtiary Volcanics. 


(2.) Conglomerates, sands, mudstone, 
lignite, 






(4.) Older rhyolites. 


(3.) Crystal tufis and flows. 






Lower Miocene — 
Trachytio breccias. 


Miocene — *Andesitio breccias, 
Beeson's Island \ tufis with lignite, 
Group. ( and flows. 




Miocene— /(I.) 'Andesitic breccias. 
Tertiarv Volcanic 
Rocks op the 


Older Pliocene 




Andbsitb Series— 
(1.) Pyroxene andesites. 
(2.) Hornblende andesites. 






■' Second Pebiod " ) 
OB Beeson's Island | 
Series. \(2.) Plow andesites. 


and lavas. 




Age (?) — 

Auriferous rooks of Thames. 


Eocene — 

(1.) Kapanga Group. 

(2.) Thames-Tokatea Group. 


Upper Eocene (?)— ((1.) Andesitic rocks. 
Tertiary Volcanic 
Rocks op the" 
"First Period." (2.) Rhyolitio rocks. 


Upper Miocene — 
Andesites and daoites. 


Older Tertiary. 




Cretaoeo-Eocene — 
Goal-measures. 


Not represented in Aroha Subdivision. 


Lower Eocene (?)— 
Torehine Series. 


Miocene — 
Oamaruian. 


Palaeozoic — 

Grauwaokes and argillites. 


Lower Cabboniperods to Uppek 
Devonian — 
Slates, sandstones, felsites. 


Triassio to Upper Devonian — 

Conglomerates, sandstones, slates with 
dykes, &o. 


Jura-Tbiassic- 

Grauwaokes and argillites. 


Jurassic and Pre- Jurassic — 

Conglomerates, grauwaokes, and argillites, with 
djkes, &o. 


Jura-Triassio. 



Oeo. Bull. No. 16.] 



* Same formation in part. 



[To lace p. 57. 



57 

Views op other Writers. 

Each writer on the geology of the Hauraki Peninsula admits the difficulties involved 
in the classificatioa of the vast accumulation of volcanic rocks which constitute the 
succession. Cox* was the first to arrive at an accurate idea of the succession of 
the volcanic rocks. He recognized three series of rocks, and all later writers have 
adopted these three series as the basis upon which their classifications are built. 
Differences arise when the distribution of each series is discussed, for, although the 
position of a rock in the succession may be perfectly clear, different writers 
would refer the rock to different series. These differences of opinion are brought 
about by a want of clearness of definition of the characteristics which should dis- 
tinguish each series. All those who have examined the district recognize this, and 
each has formulated, either in writing or in his own mind, the characteristics upon 
which he himself rehes. Thus the andesites are very generally divided according to 
the amount of alteration they may have undergone, the breccias on. their relative 
degrees of consohdation, or both upon the position they occupy in the hypothetical 
structure of the area examined. It is submitted that any classification based upon 
such considerations must be unsound, and the writer adopts a classification which is 
based chiefly upon the chemical composition of the rocks. This classification has been 
found to be applicable in the field to the rocks of the Aroha Subdivision. 

All writers who have examined the rocks of the Hauraki Peninsula are agreed 
that they are all more or less related to each other, and form as a whole a '' petro- 
graphical province." Now, a chemical classification imphes that the lavas of different 
chemical composition are not extruded haphazard, but follow a definite order of extra- 
vasation in obedience to the operation of certain laws. The order of succession 
of the rocks of many districts has been estabhshed, and Iddings| enunciates the rule 
" that in a region of eruptive activity the succession of eruptions commences in 
general with magmas representing a mean composition, and ends with those of extreme 
composition." This is the law of " increasing divergence " from the initial type, and 
the writer has found that, as far as the volcanic rocks of the Aroha Subdivision are 
concerned, the law apphes. Harker,J in discussing the chronological sequence of 
associated rock - types, concludes " that the causes which bring aboiit any important 
change in the volcanic rocks of a given centre operate with extreme slowness, as 
measured by human events." This means that each well-marked type of rock represents 
a considerable time-interval, and that a classification based upon chemical composition 
is also a classification according to age. 

The table faciag this page shows the classification of the rocks of the Cape Colville 
Peninsula adopted by the various writers. 

Trias-Jura Formation. 

ArgiUites and grauwackes, with the usual hthological gradations between these two 
more or less definite rock-species, cover an area of about twenty-one square miles 
within the subdivision. They outcrop only in the Hangawera Hills, which, being topo- 
graphically mature, do not afford good or numerous outcrops. The general strike of the 
beds appears to be a few degrees to the west of north, and the prevaiHng dip westward. 

No data by which the age of these rocks could be determined were collected, 
and a Trias-Jura age is provisionally assigned to them. 

Hochstetter, in his map of the Auckland district, dated 1859, classes these rocks 
as of Palaeozoic age. Similar rocks which are exposed near Lake Waikare, Waikato 

* (Jox, iS. H. : '■ Goldiields oi the Cape (Jolviile Peninsula," CS. Reports, vol. xv, 1883, pp. 4-61. 
t iddiugs, J. L'. : (qjiiait. Joui'. Geol. Society, vol. lii, 1890, pp. 000-17. 
j ilarkcr, A. : " The Natural History of igneous Rocks," 1909, p. 113. 



58 

district, and which are probably an extension of the rocks developed in the Hangawera 
Hills, are also assigned a Palseozoic age by Hutton* and Cox.f ParkJ maps the same 
rocks as Permo -Jurassic, and Marshal)§ as Triassic. 

The Andbsite Series. 

Distribution. 

The rocks of the Andesite Series cover an area of about sixty-three square miles 
within the Aroha Subdivision. They constitute the lowest portion of the volcanic sequence 
exposed in this portion of the Hauraki Peninsula. As already mentioned, the flow 
rocks may be referred to two main classes — hornblende andesites and pyroxene andesites 
respectively. The hornblende andesites occur in the following streams : The upper 
Waitawheta and Waipapa, the left branch of the Waimata, the Waiau Gorge, the 
Waitanui and Wairoa, the Wharawhara, Te Rere-atu-kahia, and Waitakohe streams. 
They form, moreover, the hills bounding the Waihi Plain on the east. On the western 
side of the range they are found in the Pohomihi, Wairakau, and Waipupu streams, 
but do not appear to occur farther south on this side of the range. A quartz- 
hornblende andesite is found in the Waitawheta near Dickey Flat, a little to the west 
of the Mangakino mouth, and again at the head of the Maiigaiti Stream. A similar 
rock, strongly propylitized, is found in the Ohinemuri Gorge near Karangahake Town- 
ship, and perhaps the quartz-pyroxene andesites west of Owharoa may also be included. 

Pyroxene andesites are found in the Ohinemuri Valley from the Rising Sun Claim 
to Mackaytown. They form the bulk of Karangahake Mountain, and outcrop on the 
Rotokohu Saddle. They are found in the Waitoki, and in all the creeks southward 
to Te Aroha. They form in great part the mountain-masses of Te Aroha and Ngata- 
mahinerua, and appear along the, base of the Okauia fault-scarp in the south of and 
beyond the Hmits of the area examined. Two isolated occurrences may be noted — a 
very small outcrop near the western coast of Matakana Island ; and a small patch 
of rubbly rock, doubtfully derivative from flow rock, on the Hangawera Hills. 

The fragmental rocks of this period have relatively but sm^all development. The 
principal occurrences are at Karangahake and Te Aroha in connection mth the 
pyroxene andesites, and in the basin of the Wairoa interbedded with hornblende 
andesites. Small unimportant lenses of breccia were observed in connection with the 
hornblende andesites at numerous places, among which may be mentioned the Waiau 
Gorge, the Wairoa, Wharawhara, and Wairakau streams. Similar irregular breccia 
bands occur with the pyroxene andesites, but do not appear to be so numerous as 
in the case of the hornblende andesites. 

After the extrusion of the andesites, beds consisting of grits and mudstones with 
thin seams of carbonaceous material were deposited in portions of the area. These 
beds, though of no great thickness, once covered an extensive area, but only small 
disconnected fragments of the original sheet now remain. Exjjosures may be seen 
in the valley of the Ohinemuri, where the road across the Rahu Saddle joins the 
main Paeroa-Waihi Road, and again in the valley of the Waitawheta, at Dickey 
Flat. Another very small exposure is to be seen on the left bank of the Waitawheta, 
about 35 chains above the Mangakino junction. 

Prospecting for coal has been carried out at Dickey Flat, but the carbonaceous 
deposits here, and all similar deposits throughout the peninsula, have proved worthless. 
Carbonaceous material from Tarariki Creek, from an extension of the beds occurring 



* Hutton, F. W. : " Geological Report on the Lower Waikato District," Geol. Rep., vol. ii, 1867, p. 2. 
t Cox, S. H. : " Report on Waikato District," Geol. Rep., vol. x, 1877, p. 17. 
t Park, J. : " Geology of New Zealand," 1910. 
§ Marshall, P. : " Geology of New Zealand," 1912. 





Per Cent. 


Per Cent. 




20-07* 


30-40t 


. . 


17-57 


30-38 


, . 


10-21 


17-58 


• • 


52-15 


21-64 




100-00 


100-00 


Succession. 







59 

in the Waitawheta and Ohinemuri valleys, has been examined, with the following 
results : — 

Fixed carbon 
Volatile matter 
Water 

Ash 



The hornblende andesites are undoubtedly older than the pyroxene members of 
the series. In the Wairoa Stream, the southern tributary of the Tuapiro, hornblende 
andesites carrying a few quartz phenocrysts (about one in each slice) occur from 
the confluence with the Waitanui to the junction with its right branch ; moreover, 
the upper part of the Wharawhara Stream is cut in hornblende andesite to its source, 
while, at the head of the Wairoa, many hundreds of feet above any outcrop of 
hornblende andesite, occurs a pyroxene andesite. In the Waitakohe the hornblende 
andesites which carry the lodes of this area give place to a pyroxene andesite on 
the Thompson's Track saddle at a much higher level. In the Waitawheta Valley, 
near Dickey Flat, a hornblende andesite with a little quartz occurs ; the same rock 
with more quartz outcrops near the Mangakino junction, and again at the head of 
the Mangaiti. The ridges to the west and north of these outcrops are all of pyroxene 
andesite, which occurs at a higher level than the hornblende andesite. At none of 
these places is a clear section shown, and none affords positive proof that the pyroxene 
andesites are younger than the hornblende - bearing rocks. Other facts, moreover, 
support this thesis. The distributioa of the pyroxene andesites as set forth above, 
and shown on the accompanying maps, indicates that the hornblende andesites are 
encircled by the pyroxene andesites but for two gaps. -Again, at Karangahake a 
quartz-bearing rock, which is so propyhtized as to make the original ferro-magnesian 
minerals unrecognizable, is overlain by pyroxene andesites. This section is quite clear. 
As far as the writer's observations go, numerous large corroded quartz granules occur 
in the andesites of the Aroha Subdivision only when these are hornblende-bearing, 
and for this reason it is considered that this quartz-bearing Karangahake rock was 
originally a hornblende andesite. 

For the reasons above set forth, the writer beheves that the hornblende members 
of the Andesite Series were extruded before the purely pyroxene rocks. 

Petrolocjy. 

The terms " hornblende andesite " and " pyroxene andesite " have been freely 
used, but it must be distinctly understood that no sharp Une can be drawn between 
the types. There are some andesites in which the o\\\y ferro-magnesian mineral 
developed is a greenish-brown hornblende. As is well known, the hornblende of a 
molten magma is unstable under surface conditions, and in many cases resorption 
borders of granular magnetite and augite surround the hornblendes. Some rocks 
show the merest core of hornblende set in the resorbed crystal, while in others no 
core is left at all. Such rocks always carry hypersthene as their dominant ferro- 
magnesian mineral, and often also fibrous bastite, presumably pseudomorphous after 
enstatite. Crystals with absolute certainty referable to enstatite are quite rare. 
Rocks showing under the microscope few resorbed hornblendes often carry augite, 



* Dominion Laboratory : 43rd Annual Report, 1910, p. 6. t Bulletin No. 15, 1912, p. 181. 



60 

but tMs mineral is never more abundant tlian hypersthene in such rocks. Augite is 
developed in larger quantity in rocks whicli skow no trace of kornblende-resorption 
skeletons, and in such rocks bastite is never seen. Purely augite andesites were 
not observed, and those with augite as the dominant ferro-magnesian are uncommon. 
Rocks with an approximately equal development of augite and hypersthene are common, 
perhaps more common than those showing a pre-eminence of hj'^persthene. Andesites 
carrying hypersthene as their only ferro-magnesian mineral occur, but are not common. 
In all of these types the feldspars seem to maintain a fairly steady composition 
(andesine to labradorite). The matrix, on the other hand, varies considerably. In 
those andesites which carry hornblende, with only narrow resorption-boundaries, the 
groundmass carries a great deal of glass. On the other hand, those andesites of 
which the hornblende outhnes contain small cores have a groundmass much more 
crystalhne. As a consequence of this, these rocks are hght-grey in colour, and harsh 
to the touch. Other factors, however, may affect the colour of the rock besides 
the amount of glass in the matrix ; thus tha hght-coloured rocks in hand-specimens 
seem much more porous. As a whole, the rocks carrying augite have more iron-ore 
dust in their groundmass than the hornblende-bearing rocks. 

SoUas* has described numerous andesites from among the rocks of the Aroha 
Subdivision. These are nearly all from the neighbourhood of Karangahake and Te 
Aroha. In " The Rocks of the Cape Colville Peninsula " hypersthene-augite andesites 
are described under Nos. 159, 162, 164, 210, 211, 217, 218, 219, 232, 252, and 263; 
quartz-hypersthene andesites under Nos. 238, 244, 245, and 246 ; altered andesites 
under Nos. 163, 213, 215, 234, 235, 251, 253, 254, 255, 264, 266, 267, 268, 269, 282, 
and 395. The determination of the nature of some of the rocks, here included under 
altered andesites, presents great difficulties. Some of the rocks contain phenocrysts 
of orthoclase and quartz ; and Professor SoUas, who " studied each rock independently 
as a separate problem,"t called most of such rocks rhyohtes. The orthoclase of these 
rocks, however, is of secondary origin — a sodium-bearing valencianite. Professor SoUas 
also discusses the nature of the matrix of the andesites, and distinguished two types 
— the hyalopihtic and micropoecihtic. In the hyalopihtic type the feldspar laths and 
other constituents of the groundmass are immersed in a glassy base. In the micro- 
poecihtic type the glassy base " is replaced by a mosaic of crystalhne grains. "J These 
grains are often, and probably always, quartz. The writer is constrained to differ 
from Professor SoUas on this point. In his opinion the micropoecihtic texture of the 
andesite matrix is due to the alteration of a glassy base in the first stage of propyhtization. 

The reasons for this behef are, — 

(1.) In every case where the micropoecilitic texture obtains there are indications 
that the rock is altered. Either the hypersthenes show more or less 
alteration to chlorite and serpentine or carbonates, or chloritic substances 
appear in the feldspars. 

(2.) Some rocks show patches of micropoecihtic texture in a hyalopihtic base, 
and in one case such a patchy rock passes into a rock with an entirely 
micropoecilitic groundmass. 

(3.) The matrix of some propyhtized breccias show a texture indistinguishable 
from micropoecihtic texture. 

As far as the writer's observations go, the groundmass of the unaltered andesites 
show every gradation between the hyalopihtic and pilotaxitic textures. The hyalopilitic 
is the commoner. 



* Sollas, W. J., and McKay, A. : " Rocks of tlie Cape Colville Peninsula," vols, i and ii, 1905-6 
t Op. cit., vol. i, p. 123. t Op. cit., vol. i, p. 117. 



Plate VII. 




Hypbrsthbne Quartz Andesite, showing Alteration of Groundmass dub to Propylitization. 



Reproduced from " Rocks of Caps Colville Peninsula," Vol. ii, p. 33, where the rock is called " Black 

Hypersthene Dacite." 
Geo. BiiU. No. W. \ 



\To face p. 61. 



61 

. The andesites of the Hauraki Peninsula have been described exhaustively by 
Professor Sollas, and no new types have been found within the Aroha Subdivision. 
The following description, taken from Sollas,* of a rock from the road quarry opposite 
the Crown battery, Karangahake, may be quoted : — 

" Matrix : A brownish glass, crowded with long rectangular sections of plagioclase 
of various size, . often once or twice twinned, arranged in stream-Unes ; prisms of 
pyroxene and grains of magnetite. 

" Phenocrysts. — Plagioclase : Numerous crystals, glassy-clear, with conspicuous 
inclusions of brown glass containing pyroxene microUths, often forming an irregular 
network. Sometimes zonal, generally elongated parallel to one cleavage, index of 
refraction above balsam ; extinguishing 22°/24° to 32°/34° (labradorite). 

" Hypersthene : Numerous large crystals ; pleochroism faint, salmon -pink to greenish- 
blue ; contains inclusions of colourless augite. Sometimes inclusions of plagioclase 
occur, and Uquid cavities with bubbles having a spherical form or forming negatis^e cr3'stals. 

" Augite : Faint brown. 

" Magnetite : In grains and as dendritic growths, and coarse irregular network 
in some crystals of hypersthene. 

" Clusters of phenocrysts occur in places with associated glass, or a green finely crystal- 
line material representing it, and containing long feldspar prisms having a tendency to 
radiate growth." 

The above description appUes, with little modification, to all the pyroxene andesites 
of the subdivision. 

The following description, also taken from Sollas, f is of an andesite containing 
quartz crystals, and showing the initial stage of propyUtization. The rock is from 
the first road quarry west of Owharoa : — 

" Matrix. — Feldspar laths in stream-lines, crowded' with minute granules of quartz, 
. minute prisms of pyroxene, leucoxene, and magnetite granules. Blotches of micro- 
pcecillitic structure spotted about abundantly ; in some instances a corroded phenocryst 
of quartz serves as a nucleus to one of these patches. 

" Phenocrysts. — Plagioclase : Numerous large well-formed crystals and complex 
growths, fresh, variously twinned, and which include small grains of augite ; some 
filled with a glass net, the margin remaining clear ; refraction index above balsam ; 
extinguishes 15715° to 23723° (andesine). 

" Augite : A few crystals and fragments, faint bluish-green, extinguishing up to 45°. 

" Hypersthene : A few large crystals and fragments beginning to pass into green 
serpentine. 

" Quartz : Numerous highly corroded grains without any fringe of green .augite 
crystals ; probably original. 

" Ilmenite and Magnetite : Fresh ; not passing into leucoxene." 

The hornblende-bearing andesites differ but httle from the rocks above described. 
Hornblende, often corroded, replaces the ferro-magnesian minerals to a greater or less 
degree. At the head of the Waitawheta the hornblende-bearing rocks have a great 
deal of glassy matrix, and the writer beUeves that they pass into the glassy rock 
outcropping in the Waimata Stream. This rock has been described by Sollas J as 
follows : — 

" Colourless and brown glass in straight and parallel bands ; colourless, clear, but 
densely charged with microliths arranged in stream-lines parallel to the banding ; 
the brown glass finely granular, becoming clear and colourless round the microliths, 
which are sparingly present in it. 



* Op. cU., vol. ii, 1906, p. 6. t Op. cit., vol. ii, 1906, p. 33. t Op. dt., vol. ii, 1906, p. 41. 



62 



" MiCROiiiTHS : Many are rod-like, with expanded ends, colourless, and extinguishing 
up to 45°. Some are twinned ; twinning-plane at right angles to the length. The 
twinning can only be observed by means of a quartz wedge, which in twinned crystals 
shows one end positive and the other negative. Other slender colourless rods are 
also present,, as well as small crystals of plagioclase, Avhich in one instance gave an 
extinction of 10V6° measured from synthetic twin lamella ; the index of refraction 
was found to be above that ot balsam. Trichites are absent. Some green elongated 
rods, pleochroic, extinguishing up to 9°, are probably hornblende. The specific gravity 
of the rock is about 244, as determined from small fragments." 

Sollas* describes a fine-grained tuiT which occurs in the Karangahake Railway 
tunnel and m the workings of the Ravenswood and Tahsman mines, as follows : — 

" Matrix minutely granular, crystalHne, filled with minute fragments and altered 
crystals of muscovitised feldspar pseudomorphs in chlorite, fragments of quartz, 
leucoxene granules, minute pyrites, granules and larger fragments of matrix of flow 
rocks reminding one of andesites ; but no pumice or shreds of vesicular glass now 
recognisable. The longer axis of some of the larger fragments points downwards at 
right angles to the direction of bedding." 

The specimen described is from the workings of the Ravenswood Mine, and is 
evidently propyhtized. 

The following analyses show the composition of some of the andesitic rocks of the 
subdivision : — 









{!•) 


(2.) 


(3.) 


(4-) 


(5.) 


SiOj .. 




61-83 


61-20 


59-20 


58-90 


54-90 


AI2O3 




16-68 


17-61 


17-00 


17-89 


18-23 


Fe^O., 




1-52 


4-35 


3-96 


2-67 


0-74 


FeO . . 




. 1-44 


1-33 


3-13 


3-42 


3-70 


MnO . 






0-04 


0-05 


0-08 


0-09 


0-18 


CaO . 






5-05 


4-48 


6-70 


6-40 


3-42 


MgO . 






2-40 


1-21 


302 


2-64 


4-20 


K2O . 






1-78 


1-74 


1-64 


1-75 


2-19 


Na^O . 






3-12 


3-21 


2-63 


2-92 


2-92 


TiOg . 






0-56 


0-85 


0-98 


0-78 


0-57 


P2O5 • 






0-16 


0-10 


0-25 


0-25 


. . 


FeSa . 






. . 


. . 






3-88 


CO2 . 








Nil 


Nil 


. . 


1-93 


Combined water and or 


- 










ganic matter . . 


2-43 


2-69 


1-30 


1-13 


3-44 


Moistur( 


J at 100° 


C. 


2-77 


1-38 


0-33 


1-32 


-- 



99-78 



100-20 100-22 100-16 100-30 



No. 1. Quartz-hornblende andesite from the WaitoM-Mangakino Track. The 
specimen analysed was not quite fresh. 

No. 2. Hornblende andesite with a little quartz and hypersthene, from the Wairoa 
Stream, a branch of the Tuapiro. 

No. 3. Hypersthene andesite with a small amount of augite, from Sheehan Creek. 

No. 4. Pyroxene andesite, the hypersthene and augite in about equal proportion, 
from the Waitoki-Mangakino Track. 

No. 5. Fine-bedded andesite tuff from No. 14 level, Tahsman Mine. 



* Op. cit., vol. ii. 1906, p. 26, 



63 

Age and Correlation. 

All writers are agreed that, as a whole, the andesites form the basal beds of the 
volcanic sequence of the Hauraki Peninsula. Fraser and Adams consider that some 
rhyoUtic rocks occurring in the Coromandel Subdivision are older, but state that 
there is no direct proof that they actually belong to an horizon below the andesites.* 
Again, Bell and Fraser place the spheruhtic dacite developed near Owharoa beneath 
the andesitic rocks of the same locahty.f Evidence, however, will be adduced on a 
later page to show that the rock is in reaUty younger than the andesites. 

In 1883 Cox divided the volcanic rocks of andesitic facies into an older and 
younger series, and since then all writers have adopted a similar classification. When, 
however, the various maps are compared, the distribution of the two series, even in 
well-known and easily accessible locahties, is found to differ greatly. Fraser and 
AdamsJ make use of the following criteria by which the rocks of the two series may 
be distinguished. They themselves admit, however, a great difficulty in differentiating 
the rocks in some locahties. 

(1.) Propyhtization is widespread in the andesitic rocks of the First Period. 
(2.) The lavas of the First Period usually have a micropoecilitic groundmass, 

while those of the Second Period have a hyalopihtic one. 
(3.) The breccias of the First Period are much better consohdated than those 
of the Second Period. 

It has already been pointed out that micropoecihtic texture as developed in 
the rocks of the Aroha Subdivision is not an original structure, but has been brought 
about by propyhtization. Again, it is easy to understand that propyhtization, which 
affected both lavas and fragmental rocks, and which brought about a molecular 
readjustment, would cause a consohdation of breccias, &c. Thus the three points 
of difference by which the rocks of one period may be distinguished from those of the 
other are in reahty but one — the presence or absence of propyhtization. The cause 
and characteristics of propyhtization will be discussed on a later page. It will suffice 
here to state that it is superinduced upon consohdated rocks by the circulation of 
heated solutions. Propyhtization is not confined to any particular period, and cannot 
be considered a criterion of age. As far as the microscopic structures of the andesites 
go, the present writer has found it impossible to separate the basal andesites of the 
Aroha Subdivision into two series. The chemical composition of the rocks offers no 
guide in this matter, and all the rocks of an andesitic facies (with the exception of the 
post-rhyohte dykes) are considered to form one series. This andesitic series corre- 
sponds most nearly to the " auriferous rocks " of Cox, although the spheruhtic dacites 
of Owharoa are excluded by the present writer. This series may be correlated with 
Thames-Tokatea and Kapanga groups of McKay, and also with the lower portion of his 
Beeson Island group. It includes the First Period and the older rocks of the Second 
Period of Bell and Fraser. 

The examination of the Aroha Subdivision has afforded no facts by which the 
absolute age of the andesitic rocks might be determined. They are certainly not 
older than Eocene, and the writer is inchned to regard them as of Upper Miocene age. 

The Dacite Series. 

Distribution. 

Within the subdivision rocks of a dacitic facies cover an area of about sixty-two 

square miles. Flow rocks form a very small proportion of the rocks of this series, and 

appear to be confined to the base of the succession in the central portion of the 

district. Immediately overlying the flow roclis, and in close mineralogical connection 

♦ Bulletin No. 4, 1907, p. 63. f Bulletin No. 15, 1912, p. 39. % Bulletin No. 4, 1907, pp 67 and 75. 



64 

with them, are dacitic crystal tuffs, in places grading to breccias. These rocks, with 
the flow rocks, form the lower member of the series. Overlying with apparent 
conformity are beds of soft white mudstone, which in places carry hgnite seams up to 
6 ft. in thickness. Overlying the mudstones are breccias with a sandy matrix ; many 
of the fragments contained in this are andesitic. This closes the series as far as known. 

The largest exposure of the lowest members of the series is in the basin of the 
Waitawheta. The flow rocks of this series cap the low hills between the Ohinemuri 
and Waitawheta to the west of Owharoa, and again occur in the valley of the Manga- 
kino. The rock forming the top of Karangahake Ridge is a sihcified equivalent of 
these rocks. What are believed to be crystal tuiis of this series have a great de- 
velopment in the Waitawheta Valley, from the big dyke* to beyond the Waipapa 
junction. Similar rocks occur in the Mangaldno, and may be traced continuously to its 
head, where they are propyhtized. They form the top of Te Aroha Mountain and the 
hills on its western base. The peculiar knobs between Ngatukituki and Ngatamahinerua 
mountains are of these rocks, but occasional thin bands of spheruUtic dacite also occur. 
The curious tuffs occurring at the Wairere and Waiteariki falls are doubtfully placed here. 

The mudstones have their greatest development in the Waitawheta Valley, below the 
big dyke, but do not reach beyond Dean Creek. They occur again in the valley 
of the Waimata, and there carry hgnite seams. The thin beds of mudstone in Fire- 
wood and Whare creeks probably represent the edge of this deposit. In the Waita- 
wheta, near the big dyke, the mudstones grade into sands, which in turn become 
breccias with a sandy or ashy matrix containing numerous andesite fragments. These 
beds form Maungawhio-tapu Hill and the ridge between the Waipapa- Waitawheta 
and Pohomdhi-Waiorongomai drainage-systems. They also form the hills fringing the 
Hauraki Plain near Tirohia and Mackaytown. Here also belong the breccias which 
form Pukepenga and Ariariparitapu, the central and southern peaks of the Ngata- 
mahinerua Ridge. They form great chffs in the Puketutu Stream, and probably 
extend over part of the Whakamarama Plateau. 

Succession. 

The lowest member of the series, a dacite with a glassy base in which spheruUtes 
are often developed, occurs in typical development near the mouth of the MangaMno 
Stream, and again for a distance of 30 chains exposed along the Mangakino-Karangahake 
Track. Here the rock is perfectly fresh. Farther down the Waitawheta River, 
at Dickey Flat, are carbonaceous beds upon which the dacite probably hes, but no 
clear section was seen. The country rock of the Rising Sun and the old Ruapehu 
claims at Owharoa is of this rock, here considerably propyhtized. In similar condition 
it occurs on the top of Karangahake Mountain, and, although no junction was found, 
it undoubtedly rests upon the pyroxene andesites of Karangahake. A fresh glassy 
rock is interbedded with the crystal-tuff breccia forming the knob about 20 chains 
south of the saddle of the Tuahu Track, and this rock is also found at the head of 
some of .the branches of the Waipupu. 

For reasons already mentioned, it has been found impossible to separate the 
overlying crystal tuffs from the dacites just described. These tuffs are well exposed 
in the Waitawheta above the big dyke, and also in the Mangakino. When propy- 
htized it is difficult to distinguish them from a like phase of the andesites, hence the 
mapping of these rocks upon the Te Aroha Mountain-mass must be regarded as merely 
tentative. 

The middle beds of the Dacite Series consist of horizontally disposed white mud- 
stones. They appear to rest conformably upon the crystal-tuff breccias in the 



* See page 73. 



65 

AVaitawheta, a little above the confluence with the Mangakino. In tlie \Vainiuta Creek 
the actual junction of the mudstones and Lrecciaa was not ob.served. In the .south 
branch of the Waimata Stream and in Firewood Creek the mudstone-beds are represented 
by irregularly bedded sandstones and conglomerates. A similar series of beds occurs 
in Trig, Waipapa, Whare, and Dean creeks, in the Waitawheta basin, and it seems 
probable that these beds represent the deposits near the margin of the depression in 
which the mudstones were formed. This supposition is supported by the occurrence 
of lignite seams near the transition between the mudstones and the coarser beds. In 
the Waitawheta, near the big dyke, only carbonaceous bands occur ; but in the 
Waimata lignite seams up to 6 ft.* in thickness may be observed. Seams occur in 
several horizons, but are very irregular in thickness and distribution. The hgnite 
consists of a dull earthy-looking homogeneous base, in which occur more lustrous 
bands, with brown, altered, but still tough roots and stems. 

The two following analyses (made in 1899 by P. G. Morgan) refer to samples from 
AVaimata Creek : — 

Lustrous. Homogoueous. 

Moisture . . . . . . . . 23-5 29-5 

Volatile matter . . .". . . 35-3 32-0 

Fixed carbon . . . . ' . . . . 32-6 29-7 

Ash .. .. .. " .. ..8-6 8-8 

Evaporative power . . . . . . 4-24t 3-89t 

From these analyses it will be seen that the coal is a low-grade hgnite. The 
deposit has no commercial value. 

The youngest member of the Dacite Series consists of a breccia, the matrix of 
which is hght-coloured, while most of the fragments are andesitic. In the Waita- 
wheta Valley the mudstones of the beds just described become sandy, and the gradation 
to the breccias of Mangawhio-tapu Hill is gradual. In Whare Creek and in the 
Waipapa Stream the breccias rest upon the sandstones and conglomerates of the 
Mudstone Series. In the valley of the Mangakiri and Wairoa the Mudstone Series 
is probably not represented, and the breccias rest directly upon the crystal tuffs. On 
the hills near Tirohia the base of the breccias was not observed. In Puketutu Creek 
these breccias rest directly upon pyroxene andesites. From these facts it will be 
gathered that the distribution of the breccias is rathei' wider than that of the lower 
members of the Uacite Series. 

Fe.lrolofjii. 
Professor SollasJ has xlescribed the microscopic charactei' of many samples of 
rocks belonging to the lowest member of the Dacite Series. Nearly all the samples 
described were from the neighbourhood of Owharoa. These rocks will be fouiul 
described in vol. ii of " The Rocks of the Cape Colville Peninsula," under the Nos. 20(), 
207, 208, 209, 233, 291, 296, 297, 298, 299, 300, 301, 302, 391, and 392. Rocks from 
Karangahake are described under Nos. 249, 250, and 256. These rocks have all been 
more or less altered by propylitization. Sollas calls samples of these rocks rhyohtes or 
dacites indifferently, and points out that only chemical analysis can definitely decide 
the nomenclature. 

A specimen of glassy dacite from the Mangakino-Karangahake Track may be 
described microscopically thus : — 

Matrix. — A clear colourless glass crowded with crystaUites, globuhtes, nuirgarites, 
and curved beaded trichite.s, often arranged in knots. In some sections periitic cracks 



* McKay, A., Mines Reports, 1899, C.-9, p. 26, says 10 ft. In his report he takes a very optimistic view 
of the value of theHo beds, 
f FouiKls of water. 
% Sollas, W. J., and McJ^,ay, A. : " Rocks of the Capo Uolvilk- PlmuusuIu," vols, i and ii, l!)Oo-(i. 

J — Aroha. 



66 

are numerous and spherulites rare, in others there are numerous cerviform spheruHtes 
and few perlitic cracks. The spherulites generally have as a nucleus some phenocryst 
of feldspar or quartz. 

SpJierulites are brownish in colour, and consist of branching fibres. They are often 
incomplete, in fact, complete spheres seem to be uncommon. They contain the micro- 
lites of the matrix, and were apparently the last formed of all the structures of the rock. 

Phenocrysts : Plar/ioclase, in crystals and fragments, often contain inclusions 
of brownish glass. They show twinning according to the Carlsbad, albite, and 
perichne laws, and zonary extinction. Extinction-angles, 18°/29°, 23°/26°, 30°/33°. 
Negative crystals with bubbles were observed. 

Htj-persthene : Numerous small crystals, usually well formed, show marked pleochroism, 
pinkish-brown to green. 

Hornblende : Occasional rather ragged crystals occur. Some small elongated ones 
show strong pleochroism in greenish-brown to pale-brown tones. They show no 
lesorption border. 

Quartz : Large corroded grains are not common. 

Apatite and zircon are sparingly distributed. 

Iron-ore is not abundant. 

Sections from other locaUties show small crystals of very pale-green augite (diopside). 
In some cases also the rock — for example, on the Te Rere-atu-kahia Saddle — is so 
crowded with phenocrysts that the rock approaches the " nevadite " type of Zirkel. 
The rocks of this series from Owharoa and Karangahake, described by SoUas, have a 
much more generous development of spheruhtic structure than those of the other 
localities within the subdivision. The glassy matrix alters very readily, apparently 
by some form of devitrification. 

In the field the crystal tuffs, as already mentioned, closely resemble some phases 
of the flow dacites, and may only be distinguished by the occurrence of angular 
fragments. Under the microscope, in some cases, a similar difficulty in distinguishing 
the rocks obtains, the granular basis of the tuffs simulating the devitrified glass of the 
flow rock. Broken crystals are common in the tuffs, but the crystals in the flow 
are often incomplete also. It is only when spheruUtes occur that one may be sure 
that the rock is a flow. 

In the southern portion of the area described, undoubted tuffs showing characteristic 
glass fragments occur. The phenocrysts are brownish-green hornblendes, hypersthene, 
occasional small augite, quartz, and feldspar ; the feldspar crystals outnumbering the 
others combined. They extinguish at 24°/25°, 16°/19°, andesine and labradorite being 
therefore indicated. Numerous crystal fragments occur. 

The mudstones and upper breccias of the Dacite Series call for no special mention 
under this -head. 

In an appendix* to the " Rocks of the Cape Colville Peninsula " the following 
silica determinations of dacitic rocks from the Aroha Subdivision are given : — 

Rock from — 

Ruapehu Claim, Owharoa, described in Jvol.'i ii,^ p. 3,1 No. 207, contains! silica 

69-77 per cent. tt3 116^8 ^^ 

South side of Ohinemuri River, at suspension bridge below Owharoa, described 

in vol. ii, p. 24, No. 233, contains siHca 63-95 per cent. 
Door Tunnel, Owharoa, described in vol. ii, p. 68, No. 296, contains sihca 

66-56 per cent. 
Door Tunnel, Owharoa, described in vol. ii, p. 69, No. 297, contains silica 
66-09 per cent. 

* Sollas, W. J., and McKay, A. : " Rocks of the Cape Colville Peninsula," vol. ii- 1906, pp. 203-4. 



67 



ii, p. 71, No. 301, contains «ilica 



Tlie 



(1.) 

68-50 


(2.) 
62-85 , 


66-31 


14-29 


15-17 


16-22 


1-80 


4-78 


1-14 


1-23 


1-59 


2-34 


0-05 


0-07 


0-05 


2-78 


5-35 


3-84 


0-88 


1-83 


0-85 


2-92 


2-42 


2-27 


3-12 


2-56 


3-95 


0-34 


0-55 


0-54 


0-28 ■ 


0-32 


0-21 


3-74 


2-32 


2-32 


0-30 


0-30 


0-14 



Dooi' Tunnel, Owliaroa, described in vol. 

. 66-89 per cent. 
Ruapehu Claim, Owharoa, described in vol.- ii, p. 137, No. 392, contains silica 
73-56 per cent. 
All these determinations refer to the spherulitic dacite of the Owharoa district, 
rocks are all more or less altered, and No. 392 is sUghtly sihcified. 

The following analyses of rocks of the Dacite Series may be tabulated : — 

SiO, 

Al,03 

Fe,03 

FeO 

MnO 

CaO 

MgO 

K^O 

Na^O 

TiO, 

P2O5 

Combined water and organic matter 

Moisture at 100° C. . . 

100-23 100-11 100-18 

No. 1. From an exposure of glassy dacite on the Mangakino-Karangaliake 
Track, about 100 chains from the Mangakino-Waitawheta junction. 
The rock is quite fresh. 
No. 2. Crystal tuff from near Kauri Timber Company's camp, Waitawheta 

River. 
No. 3. Crystal tuff from below the Te Ariki Falls. . 
These analyses show clearly that these rocks must be classed as dacites, and not 
as rhyoUtes. 

Age and Correlation. 
Cox* in 1882 correlated the propylitized rocks exposed at Owharoa (spherulitic 
dacites) with the reef-bearing andesites of Thames and Te Aroha. Parkf in 1897 
mapped the same rocks as belonging to the " great gold-bearing series " of Upper 
Eocene age. McKay J in 1905 placed the Owharoa rocks in his Kapanga group, 
but the spheruhtic rocks of Karangahake Mountain, which he was the first to note, 
he placed in the Thames-Tokatea group, along with the andesites of the Waitawheta 
Gorge. Bell and Fraser§ consider that the Owharoa rocks are older than the 
andesitic rocks .of their First Period. These writers all correlate the Owharoa rocks 
with the reef-containing andesites of the Hauraki Peninsula. The present writer has 
found that the propyhtized rocks of Owharoa may be traced into fresh glassy dacites, 
which almost certainly overhe carbonaceous beds resting upon andesitic rocks. The 
spheruhtic rocks of Karangahake Mountain, which cannot be separated from the 
Owharoa rocks, undoubtedly overhe the andesites. The fresh glassy dacites of this 
series are closely comparable, both macroscopically and microscopically, with similar 



♦Cox, S. H. : Geological Repoi-ts, vol. xv, J 881!, p. 14. 

t Park, J. : " Geology and Veins of the Hauraki (Joldficlilfs," Trans. N.Z. lust. Miii, Kug.. vol. i. KSOT. 
j McKay, A., and Sollas, W. J. : " Rooks of the Capo Colville Ppninsula."' lOOo-li. vol. vii, pp. W> and oO. 
§ Bell, J. M., and Fraser, 0. : Bulletin No. 1.5, I!tl2. p. 41. 

6* — Aroha" 



68 

rocks from Omahu and Tairua.* These latter rocks Bell and Fraser, as well as 
BIcKay, place among the rhyolitic rocks of the peninsula. McKayf also considers 
the white mudstones of the Waimata, containing hgnite seams, as belonging to his 
rhyohtic group. These mudstones in the Waitawheta overlie crystal tuff and breccia, 
which in turn rest upon the spheruhtic dacites. In regard to the breccias with sandy 
matrix developed near Tirohia, CoxJ correlated them with similar rocks on Be'eson 
Island, near Coromandel, and considered them equivalent to the breccias of Manukau 
Harbour, near Auckland. He was the first to perceive that they were younger than 
the andesites of the peninsula ; and these rocks, excluding all lavas except younger 
dykes and flows therefrom, formed his Miocene group. 

The Rhyolite Series. 
Distribution. 
Rocks of a rhyohtic nature cover an area of about 111 square miles within 
the Aroha Subdivision. Their chief development is in the eastern portion of the 
district, and within the basin of the Waihi Plain. Long ago McKay noted a small 
outcrop of these rocks near Mackaytown, on the western side of the range, and they 
also cap the hills overlooking the Hauraki Plain north of the Hikutaia River. A 
few boulders of the pecuUar rhyolitic rock " wilsonite," found in the beds of the Pohomihi 
and Waiorongomai streams, indicate the once wider distribution of this rock. 

Succession. 

The rhyohtic rocks of the subdivision belong to two periods of eruption. This 
statement is based not upon stratigraphical evidence, for nowhere was the junction 
between the two groups observed, but upon the differences in chemical composition 
and petrographical texture shown by the members of the two groups. Even the 
relative age of the divisions is not beyond doubt, and the writer follows the sequence 
adopted by McKay, Park, and Morgan. In both periods extrusions of lava took 
place. The sequence of the older rhyohtic rocks as exposed in the upper portion of 
the Waiau Valley shows that the basal beds, here overlying hypersthene-hornblende 
andesites, are pumiceous tuffs carrying occasional fragments of andesite and pumice. 
Overlying these tuffs is a bed of crumbly perhtic rhyolite not more than 20 ft. or 30 ft. 
in thickness. This is followed by a rhyohte breccia, which is here poorly developed, 
but which at other places is seen to carry fragments of andesite, pumice, and perhtic 
rhyohte. Within this breccia are also developed conglomerate beds with carbonaceous 
bands. The sequence is closed by the massive spheruhtic rhyohte which forms 
Mount Hikurangi. Nowhere else within the subdivision is the sequence of these older 
rocks so well exposed, and nowhere else are the rocks upon which they rest to be 
seen. The older spheruhtic rhyohte occurs at Te Ho, Maunganui Mount, Minden 
Peak, and Te Kopukairoa on the mainland, while the islands of Te Karewa and Motu 
Otau are also composed of a similar rock. 

The rhyohtes of the younger group occur typically in the Waihi Plain, where they 
consist of tuff and breccia overlain by a hthoidal flow rhyohte. Nearly opposite the 
Rising Sun adit, on the south side of the Ohinemuri, this hthoidal rock is seen to 
overhe the spheruhtic dacite in which the lodes of the claim are found. The relation 
of the rhyohtic tuff " wilsonite," which forms the banks of the river to the eastward of 
this hthoidal rhyohte, is obscure in this locahty, but may be examined above Waikino 
near the quarries on both sides of the river. These quarries are in flow rhyohte, 

* For descriptions ul some of these rocks see " Rocks of the Cape ColvDle Peninsula," vol. ii, Nos. 209. 
210, 212, 221, 230, &c. Parcittl analyses are given in vol. ii, p. 203. 

t McKay, A. : " On the Occiu-rence of Coal near Waihi," Mines Reports, 1899, C.-9, p. 26. 
i Cox, S. H. : Geological Reports, vol. xv, 1883, p. 18. 



69 

which overHes the " wilsonite," the plane of contact clipping to the west. Near VVaihl 
a similar sequence may be observed. 

A much more extensive area of rocks, referred to the group of younger rhyoUtes, 
flanks the range on the side facing the Bay of Plenty. The series here consists of tuffs 
and breccias, which grade into subaqueous beds consisting of rhyolitic material. The 
exact relationship of these beds to the other beds of the younger group of rhyolites is 
not known. Eight miles west of Tauranga they wrap round and overUe Mount Minden, 
which is a mass of spheruhtic rhyolite belonging to the older group of the Rhyohte 
Series. It is upon this fact, and upon the close resemblance the basal portions of 
these beds in some locahties — for example, Aongatete, Ruangarara, and Te Puke — 
bear to the " wilsonite" tuff, that their position in the series has been determined. The 
subaqueous portions of the beds are the youngest, and grade into and in places are 
indistinguishable from the overlying Tauranga Beds described on a later page. 

Petrology of the Older Rhyolites. 

The tuffs and breccias forming the lower portion of the Rhyolite Series call for 
no special description. The crumbly perhtic rhyolite is so friable that it was found 
impossible to prepare microscopic sections. The massive spheruhtic rhyoUtes which 
close the older members of the series vary considerably in character. They are 
always spheruhtic, sometimes minutely so, and then show flow structure and banding 
prominently. The rocks with coarser spheruhtic structure weather to a light i^inkish- 
grey granular rock simulating weathered granite. In fresh specimens this rock is greyish 
in colour, and shows numerous quartz and feldspar grains and occasional flakes of biotite. 

Under the microscope the spheruhtic matrix is seen to form the bulk of the rock. 
A few radiate trichites occur, and nests of tridymite may often be seen between the 
spheruhtes. The phenocrysts are of orthoclase (often decomposed), quartz, and deep- 
brown biotite. 

Rutley,* Sollas,f and Morgan J have described these rocks. 

The following analyses show the composition of the older rhyolitic rocks : 



SiOa 

Al.O, 

Fe,0,,, 

Feb 

MnO 

CaO 

MgO 

KoO 

Na.O 

TiO^ 

P2O5 

CO, 

Combined water and organic matter 

Moisture at 100° C. . . 



lOO-l.") 100-1.^) 100-15 

No. 1. Crumbly perhtic rhyolite from the upper Wninu V'.illey. 
No. 2. Bulletin No. 15, page 48. 
No. 3. Bulletin No. 4, page 87. 



(1.) 


(2.) 


(.■!.) 


74-73 


73-70 


72-40 


10-82 


12-96 


14-09 


2-46 


2-20 


0-48 


0-.58 


0-36 


2-52 


0-03 


Nil 


0-42 


0-80 


1-42 


M5 


0-20 


0-75 


0-20 


4-40 


4 -.50 


4-09 


2-68 


2-f6 


2-97 


012 


014 


0-15 


0-12 


, , 




Nil 


Nil 


0-82 


2-94 


2-00 


0-86 


0-27 







* Rutley, F. : " Kniptivo Rooks from Now Zealand," Quart. Jourii. (Jeol. Soc, vol. Ivi. lOOO, jip. 498-.')01. 
t SoUa.s W. J., and McKay, A. : " Rocks of the Cap;- Coiville Peninsula." vol. ii. 100(i. pp. i:i2-:}:5. 
j Morgan, P. O. : " Igneous Rooks of the Wailii doldfirhl," Trans., vol. \liii, 1010. p. 272. 



70 

Petrology of the Younger RhyoUtes. 

One of the most interesting rocks of tlie whole subdivision is the rock known 
locally as " wilsonite." It occurs typically in the neighbourhood of Owharoa, where 
it is quarried for road-metal. The rock is here light-grey, with a very faint pinkish 
tint, with abundant lenticular streaks of black glass lying in general parallelism. 
Fragments of pumice and small angular inclusions of andesite are abundantly and 
regularly scattered throughout. 

McKay,* Park,| Morgan,^ Bell and Fraser,§ all regard this rock as a flow rhyolite 
brecciated by movement after partial consolidation. Kutley|| and Lindgren^ call the 
rock a breccia or tuff. SoUas** is very doubtful of its nature, but seems to incline 
to the opinion that the rock is a tuff. 

Rutley has described specimens of this rock in his two papers on the rocks of the 
Hauraki Peninsula and Rotorua. In the first paper the " wilsonite " is described under 
the No. H 8,f I and in the second paper under Nos. H 23 and H 24. Jt 

Sollas§§ has also described examples under the Nos. 265, 27.5, 294, and 393. The 
following description|||| may be quoted : — 

" Matrix. — White Portion : Glass, colourless clear to faintly brown, ultra-micro- 
scopic granular, drawn out and broken into forms usually taken as distinctive of tuff. 
The interstices between these are filled with a scaly granular material, which is 
isotropic, brownish by transmitted and white by reflected Ught. 

" Black Portion : Colourless clear to brownish, ultra-microscopic granular glass, with 
slender thread-hke vapour cavities running in stream-lines, and perhtic structure. The 
stream-lines of these fragments may correspond with those of the rock in general or 
not ; sometimes they are directed at right angles to the general flow, but the long axis 
of the whole fragment runs even then with the stream-Mnes. 

" Phenogrysts : These are present both in the white and black fragments. 

" Plagioclase, : Well-formed crystals and fragments, chiefly fragments in the white 
portion ; sometimes zonal ; synthetic twinning ; extinction, 12°/19°, 19°/20° (oUgoclase- 
andesine) ; refractive index in one instance greater than that of balsam. 

" Pyroxene : One well-formed crystal represented by a pseudomorph in chlorite, 
with associated magnetite ; also a few rare fragments. , 

" Biotite : A few well-worn crystals in process of alteration and corrosion ; pleochroism 
deep ohve-green, almost black to straw-yellow. 

" Quartz : Numerous fragments and coryoded grains. 

* McKay, A. : "Report on the Cxeology of the Cape Colville Penisnula," Mines Report, 1897, C.-9, 
p. 67. 

t Park, J., and Rutley, 1<\ : " Rhyolite.s of the Hauraki Goldfields," Quart. Jour. Geol. Soc, vol. Iv 
1899, p. 450. 

X Morgan, P. G. : " The Igneous Rocks of the Waihi Goldfleld." Trans., vol. xliii, 1910, p. 272. 

§ Bel], J. M., and Fraser, C. : Bulletin No. 15 (New Series), p. 48. 
• II Rutley, F., and Park, J. : " Rhyolites of the Hauraki Goldfields," Quart. Jour. Geol. Soc, vol. Iv, 
1899, pp. 449-69. Numerous descriptions detailed later. 

T[ Lindgren, Waldemar : " Tlie Hauraki Goldfields, New Zealand." Eng. and Min. Jour., New York, 
vol. Ixxix, 1905, p. 218. 

** Sollas, W. J., and McKay, A. : " Rocks of the Cape Colville Peninsula," vol. i, 1905, p. 123. 

ft Rutlev, F., and Park, J.: "Rhyolites of the Hauraki Goldfields," Quart. Join-. Geol. Soc, vol. Iv, 
]899, p. 457.' 

±1 Rutley, F. : " Eruptive Rocks from New Zealand," Quart. Jom'. Geol. Soc, vol. Ivi, 1900, pp. 494-95. 

§§ Sollas," W. J., and McKay, A. : " Rocks of the Cape Colville Penmsula," vols, i and ii, 1905-6. 

nil Op. cit., vol. ii, 1906, p. 46. 



Plate VIII. 

















•* t >% 



^,.^~^' ^' 



-* . ■'~.r»Ka 






"-?<.''»-. 



WiLSONITE. KePLECTED LiGHT. 10 DIAMETERS. 




Wll.SONITE. ThANSMI'I'TKU Li 



CUT. l-l DI.AMlOTEItS. 



Illustrations reproduced from " Uocks of Cape Colvillc Peninsula," Vol. i, p. (if). 



rSvo. Bull. A'o. 10.} 



[To face p. 70. 



71 

" Xenoliths. — A few small foreign fragments are included, as follows : Fragments 
of positive spherulitic growths ; groundmass of an andesic appearance ; brown glass 
with rectangles of plagioclase, chloritic pseudomorphs after pyroxene, magnetic grains ; 
groundmass consisting of long feldspar laths with a tendency to radiate growth, 
interstitial serpentine after pyroxene and interstitial quartz. 

" If, as the field evidence seems to suggest, and as the general appearance of the 
hand-specimens also suggests, this is a flow rock, then the form of the shreds of glass 
can no longer be regarded -as distinctive of a tuff. Doubts have already in other 
cases been thrown on conclusions drawn from this character." 

Professor Sollas, however, qualifies this last statement, and in a footnote of his 
accompanying report says, " Some of the specimens are formed of material which has 
fallen though the air, and seems to have retained its viscosity up to the time of 
reaching the ground."* 

Morgan| has also described this rock. 

The evidence upon which the suggestion that this rock is a flow rock appears to 
be based is as follows : — 

(1.) Field evidence: This is nowhere clearly stated, but seems to be evidence 
upon which Park and McKay rely. 

(2.) Appearance of rock in some localities : The rock when fresh, especially 
at Owharoa, has a vitreous appearance, quite unlike the usual earthy 
appearance of tuffs. The general parallehsm of the black lensoids of glass 
imparts a flow-hke structure to the rock. 

(3.) Microscopic evidence : The continuity of the stream-Hnes in the fragments 
with those in the matrix. Flow hues wrap completely round some frag- 
ments. Those who regard the rock as a flow rock consider that it 
has been brecciated by flow movement after partial consoHdation. 

On the other hand, the evidence upon which a clastic origin of the rock is based 

is as follows : — 

(1.) Field evidence : The field evidence is as much in favour of the rock being 
a tuff as of its being a lava. 

(2.) Whenever weathered the rock has the appearance of a pumiceous breccia, 
and in many locaUties, as in the upper valley of the Tieri and in the 
lower course of the Mangakiri, the unweathered rock is also very like a 
breccia. At all exposures the rock contains angular fragments of pumice 
and numerous small pieces of andesite. 

(3.) Under the microscope every section shows the matrix to consist of glass 
fragments, with the shapes characteristic of tuft" fragments, embedded 
in a granular isotropic base. 

If the rock is a brecciated flow rhyoUte, " then the form of the shreds of glass 
can no longer be regarded as distinctive of a tufl^," while the granular isotropic base 
" may be merely an alteration-product of a glass which was the last element to con 
solidate, and of a more unstable character than that which forms the brown shreds 
. . . the fluidity of this residual glass, as well as its instabiUty, were due to its 
included water."J This requires that the latest product of consolidation of a lava- 



* Sollas, W. J., and McKay, A. : " Rocks of the Cape Colville Peninsula," vol. i, 1905, p. 123. 

t Morgan, P. G. : " Igneous Rocks of the Waihi Goldfield," Trans., vol. xliii, 1910, p. 272. 

i Sollas, W. J., and McKay, A. : " Rocks of the Cape Colville Peninsula," vol. ii, 1900, p. 138, No. 393. 



72 

flow, from which already glass had consolidated after extrusion, shall contain more 
water than the glass which first consohdated. This seems difficult to understand. 
If the explanation be granted, why should minute fragments of glass with the thinnest 
of edges maintain their individuality when embedded in molten glass rich in that 
most powerful flux, water ? The black lenses of glass embedded in subparallel manner 
in the rock must have been viscous up to the latest movement ; and the question 
may be asked, why should the molten residual glass rich in water be sharply separated 
from the black glass which must have been molten at the same time ? The constant 
content of andesite fragments is also very difficult to explain satisfactorily on the 
assumption that the rock is a flow rhyolite. It will thus be seen that there are very 
grave difficulties in the way of accepting the explanation that " wilsonite "is a brecciated 
flow rhyolite. 

On the other hand, if the rock be assumed to be a tuff — and this is the opinion of 
the present writer — it is necessary to account for the lenses of black glass and also 
the vitreous appearance of the rock. The glass lenses may be regarded as lapilli 
of glass which still retained their viscosity and flattened out when they reached the 
ground. The smaller fragments, although firm enough to retain their shape, were 
sufficiently hot to frit together and produce the vitreous appearance mentioned. This 
explanation involves deposition very close to the point of ejection. In that case 
eruption took place along a line joining Waikino and Waihi. 

The flow rock overlying the " wilsonite " is, as far as the Hauraki Peninsula is con- 
cerned, of a type found only on the Waihi Plain in close connection with the " wilsonite." 
Rutley has described this rock under Nos. H 9, H 10, H 11, H 12, H 1.3, H 14, and H 16 
in his first* and as H21 in his second paper.f The following description* by Rutlej' 
of a rock from Waikino may be quoted : — 

" A pale yellowish-grey or buff-coloured lithoidal rock containing minute crystals, 
some of which are colourless and glassy, while others are dark-green or black. The 
section, under the microscope, is seen to contain corroded porphyritic crystals and 
fragments of ohgoclase, and occasionally of labradorite and andesine. There are also 
a few fragments of crystals of pale-greenish hornblende, but the pleochroism is 
extremely feeble or barely perceptible, and it is mainly on account of the extinction- 
angle that the crystals cannot be mistaken for pyroxene. Unfortunately, the shde 
shows no transverse section of these prisms, and thus the angle of intersection of 
the cleavages cannot be ascertained. The crystals are crossed by transverse fissures, as 
in actinohte. The rock itself is a lithoidal rhyohte, with rather poorly-defined corrugated 
fluxion-structure, and containing small nests of tridymite and occasional crystals and 
irregular aggregates of magnetite and pyrites. A few small rock-fragments are present 
in this lava. Some of them contain a large amount of vitreous matter, often with 
numerous microHtes and grains of magnetite. It seems probable that these small 
fragments of rock, as well as the larger fragments of crystals of the more basic 
plagioclastic feldspars and those of hornblende, were derived from andesite. These 
included fragments may be perhaps regarded as sufficient warrant for terming the 
rock a tufaceous rhyohte, but they are not very numerous, and probably indicate a 
mere sprinkhng of volcanic dust." 

Sollas,J who has described this rock under Nos. 221 and 236, considers the ground- 
mass to be axiohtic. 

This rock is the " tridymite rhyohte " of Morgan. § 

* Rutley, F., and Park, J. : " Rhyolites of the Hauraki Goldfields," Quart. Jour. Geol. Soc, vol. Iv. 
1899, pp. 449-69. 

t Rutley, F. : " Eruptive Rooks from New Zealand," Quart. Jour. Geol. Soc, vol. Ivi, 1900, p. 493. 
j SoUas, W. J., and McKay, A. : " Rocks of the Cape Colville Peninsula," vols, i and ii, 190.5-6. 
§ Morgan, P. G. : " Igneous Rocks of the Waihi Goldfield," Trans., vol. xliii, 1910, p. 273. 



73 



The following analyses of the younger rhyohtes may be 



SiO, . 
Al^O, 
Fe^O., 
FeO . 
MnO . 
CaO . 
BaO . 
MgO . 
K,0 . 
Na^O 
TiOg . 

SO3 . 

Combined watei' and organic matter 

Water at 100° C. 



Specific gravity 



e quoted : — 




(1.) 


(2.) 


72-30 


73-08 


12-50 


13-50 


2-12 


2-60 


0-47 


0-13 


0-03 


Trace 


1-35 


1-07 


, , 


0-06 


0-10 


0-15 


3-58 


3-19 


3-25 


3-95 


012 


0-62 


0-31 


Trace 




0-12 


3-54 


1-33 


0-46 




10013 


99-80 



2-514 



No. 1. " Wilsonite," from the quarry on the road on the right bank of Tieri Creek, 
a few chains from the jimction with the Ohinemuri. The sample is quite 
fresh. 

No. 2. Lithoidal rhyohte, 100 ft. level, Grand Junction Mine, Waihi. The ground 
sample was dried at 100° C. before analysis. Analyst, Phillip Holland.* 

Age and Correlation. 

It is generally agreed that the rocks of a rhyohtic facies are younger than the 
andesites and dacites. The exceptions to this statement have already been discussed 
(see p. 63). Parkf correlates the rhyohtic rocks of the Hauraki Peninsula with the 
similar acid rocks of the " Taupo Zone." This question will be discussed on a later 
page. All writers agree in assigning the rhyolites to the Phocene period. 



The Dyke Series. 

Distribution. 

The largest dyke within the subdivision is the great dyke crossing the Waitawheta 
about twelve miles in a straight line south-south-west from Karangahake. This dyke, 
between its walls, is here nearly 60 chains in width. It may be traced westward into and 
beyond the valley of the Romunga, but was not observed in the -Mangakino Stream. 
Eastward it appears as far as the Waitanui, and the large dyke in the Wairoa may be 
regarded as an extension. Evidently the lava which forms this dyke found access to 
the surface. The flow seems to have been chiefly to the north, and to have proceeded 
from several points of issue. This eruption must have had many resemblances to a 
fissure eruption, and in this connection it may be pointed out that no breccia appears to 
have been formed in connection with this dyke. The flow spread over a surface upon 



* Rutley, F., and Park. .J. 
1899, p. 467. 

-f Op. cit., p. ^'jl. 



" Rhyolite.s of the Hauraki Goldfields," Quart. .Tourn. Geol. Soc, vol. Iv, 



74 

■which vegetation was established, as shown by the carbonaceous material separating the 
flow andesite from the irregular denuded surface of the mudstone in the Romunga Creek. 
The walls of the dyke in the Waitawheta are in part formed of the breccias of the 
dacitic series, showing that it is younger than these breccias. It was nowhere observed 
to overlie these breccias, and probably the flow followed valleys cut below the breccias 
in the old surface. 

Other dykes petrologically similar, and striking, as far as could be ascertained, in 
directions subparallel to the large djke in the Waitawheta, occur within the subdivision. 
Such is the dyke forming the southern boundary of the Waihi Plain from the 
Mangakiri to the Waimata, and tlie dykes crossing the Waiau and Wairoa streams. 
Small dykes occur in the Wairakau and Wharawhara. 

PeXrology. 

Sollas has described a specimen of rock from Mangakiri Creek, probably from part of 
the large dyke crossing that creek, as follows* : — 

" Matrix : Forms the greater part of the rock, brownish granular glass densely 
charged with plagioclase laths of all sizes, from minute microHths up to large planks, 
lying in stream-hnes, with abundant prisms of augite and hypersthene, and minute 
octahedra of magnetite. The plagioclase extinguishes at 21°/21° (andesine), frequently 
presents forked or ragged ends, and is sometimes filled with glass. Tridymite is also 
present. 

" Phenoceysts. — Plagioclase : Large crystals and complexes, not numerous ; 
generally rich in inclusions, fiUing the interior along parallel lines as a kind of network, 
but always leaving the marginal zone clear ; refractive index above balsam ; extinguishes 
from 18°/18° to 30°/30° (andesine-labradorite). The inclusions consist for the most 
part of pyroxene and glass. 

" Aiigite : Small crystals, faint-green tint, extinguishes up to 45°. 

" Hypersthene : More abundant than augite, fresh, with the usual pleochroism. 
Some extraordinary intergrowths of hypersthene and augite occur. Numerous small 
prisms of hypersthene, lying for the most part parallel, but not wholly so. are shot 
through with augite to form a complex, the augite of which extinguishes simultaneously, 
as does the hypersthene which Ues parallel. Cavities hned by tridymite and filled with 
glass, as well as crystals of plagioclase, augite, and a green undetermined roineral are 
included within this network growth. 

" Olivine : Numerous small crystals of oh vine, with a reaction border formed of 
hypersthene and magnetite, the latter in the curious dendritic forms which have been 
figured by Judd." 

Professor SoUas calls the rock a hypersthene andesite or hypersthene basalt. 

This description apphes to the rock forming the big dyke and the flow therefrom, 
and also to most of the other dykes belonging to the series — for example, those in the 
Waimata, Wairoa, and Waiau streams. Quartz grains often occur, sometimes with 
reaction borders of augite and magnetite. Sometimes also the oUvine granules are 
completely resorbed, and only the magnetite grains suggest them. The constant 
characteristic by which this rock may be recognized in thin sections hes in the nature 
of the groundmass. The structure approaches the intersertal, in that the feldspar 
laths are strictly idiomorphic to the augite and hypersthene prisms. Some of the 



* SoUas, W. J., and McKay, A. : " Rocks of the Cape Colville Peninsula," vol. ii, 1906. p. 30, No. 242. 



75 

smaller dykes — for example, those in the Wairakau and Wharawhara streams — have a 
groundmass of glass in which definite feldspar laths are developed, but in which only 
incipient forms of growth represent the pyroxene prisms so numerous in the matrix of 
the rock from the larger dykes. 

The following analyses show the composition of the rocks belonging to this series : — 



SiOg 

AI263 

FeoO., 

FeO 

MnO 

CaO 

MgO 

K,0 

NajO 

TiO., 

Combined water and organic matter 
Moisture at 100'' ('. . . 



61-30 
16-31 
2-68 
4-14 
0-09 
6-65 
2-65 
1-70 
2-58 
0-60 
0-22 
0-54 
0-75 



(2.) 
59-35 
17-85 
5-92 
1-23 
0-05 
7-72 
2-02 
1-41 
2-55 
0-75 
0-16 
0-70 
0-44 



(3.) 
59-29 
17-71 
1-98 
3-78 
0-03 
6-63 
3-21 
1-54 
2-81 
0-93 
0-11 
1-46 
0-73 



100-21 100-15 100-21 

No. 1. The specimen analysed is from the head of Romunga Creek, and is part of 
the big dyke. 

No. 2. The specimen is from the small gorge made by the Waimata through a 
dyke before it enters the Waihi Plain. 

No. 3. The specimen is from one of the small dykes which cross Wairakau Creek 
near the head of the stream. This dyke has a glassy base. 



Age and Correlation. 

The close resemblance of the larger dykes in mineralogical composition and petro- 
graphical texture, and of all the dykes in chemical composition, combined with their 
constancy of orientation, leave no room for doubt that all the dykes of the subdivision 
included within this series are of approximately the same age. This granted, their 
relative age is readily fixed, for in the valleys of the Waiau and Waitanui sections are 
exposed showing that the dykes of these localities break through the rhyohtic tuffs. On 
the southern boundary of the Waihi Plain, where the Mangaldri and Waimata break 
through a large dyke, the sections are not clear. The relationship of the dykes to the 
Tauranga Series is nowhere shown within the subdivision. The difference in composition 
between the rhyoUte and the andesite of the Dyke Series suggests a time-interval 
between their emission. T^hus the dykes were probably intruded later than the formation 
of the Tauranga Beds. 

The Tauranga and Walton Bk1)«. 
Distribution. 

The Tauranga Beds cover a considerable area* of the lowlands in the neighbourhood 
of Tauranga, and extend continuously as far north as the Waiau Stream. The fertile 
portion of Matakana Island (Matakana proper) and Motuhoa are formed of these beds, 
and also a small area contiguous with Te Ho (Katikati Heads). 



' About eighty-two square miles. 



76 

That these beds once covered a much larger area there is httle reason to doubt. 
Cox* reports the Tauranga sands as occurring at Opotiki and at various points along the 
Bay of Plenty coast. Motiti, a flat low-lying island, fifteen miles from Tauranga, is 
also probably formed of these beds. 

The Walton Beds occur in the south-west corner of the Wairere Survey District, 
where they form rolUng downs of low reUef. These beds have a considerable extension 
to the southward, where they form the Eichmond and Cambridge downs. The high-level 
terraces which occur at various places along the western scarp of the Cape Colville 
Eange, and especially just to the north of Te Aroha, r&ay perhaps be here included. 

Successio7i. 

The beds consist of conglomerates, sandstones, and clays, the conglomerates being 
the basal beds. The sands are rather poorly consolidated, and in many places show 
current bedding ; a good deal of pumice is often included. The clays at the northern 
end of Tauranga Harbour are usually yellow ; but at the southern end, where the chief 
development of these beds occurs, white pipeclays are common. The whole succession 
suggests shallow-water deposition, and the beds were probably laid down in a wide 
estuary or bay. No fossils save plant-remains were noted. 

Towards the base of the series, but above the conglomerates, seams of hghite occur. 
There appear to be two basins of coal. The northern or Whatakao basin shows 
outcrops in the valley of the Whatakao and Wainui streams. The maximum observed 
thickness of the coal was 13 ft., but the outcrops show considerable and rapid variation. 
The southern or Omokoroa basin shows outcrops on Matakana and Motuhoa islands, on 
Omokoroa Point, and in the Te Puna Estuary. The coal of this basin is 14 ft. thick 
at Omokoroa Point, 4 ft. on Matakana Island, and narrows to 1 ft. near the road 
crossing the Te Puna. The coal in both basins is horizontally disposed, but the 
disposition of the outcrops shows that the Whatakao seam must be shghtly inchned, 
with a dip to the north. The coal-forming vegetation has apparently accumulated in 
place. At Omokoroa Point, where for many chains the seam outcrops between high 
and low water mark, tree stumps and roots in their natural position, and still retaining 
some toughness and semblance of woody structure, are set in brown, homogeneous, 
carbonaceous matter. In one case a large fallen tree-trunk may be seen. Scattered 
throughout the structureless mass are fragments of plants, leaves, twigs, and larger 
branches. The " swamp growth in place " theory would account well for the formation 
of these seams. There is more or less of a carbonaceous underclay showing wherever 
the bottom of the seam could be observed. If this theory be accepted, the swamps, 
the vegetation of which is now represented by the coal-seams, filled elongated estuary- 
hke depressions. 

The following proximate analysis of a sample from an outcrop of the Whatakao 
seam showing 6 ft. of coal indicates the composition of the coal : — 

Fixed carbon ■ . . . . . . . . . . . . 17-18 

Volatile hydrocarbons . . . . . . . . . . 36-69 

Water .. .. ... .. .. .. .. 43-53 

Ash .. .. .. .. .. .. .. 2-60 



100-00 
Total sulphur . . . . ... . . . . 0-34 

* Cox, S. H. : " Report on Country between Opotiki and East Cape," Geol. Reports, vol. x, 1870-77, p. ]0S. 



77 

The beds at Walton consist of sands and clays. The sands show current bcddinj,', 
and contain pumice. The whole succession is strongly suggestive of deposition under 
estuarine conditions. 

Age and Correlation. 

The correlation of the Tauranga and Walton Beds is made because of their general 
lithological similarity. No fossils other than plant-remains were found in either group 
of deposits. The Tauranga Beds present a succession similar to that of the lignite- 
bearing beds of Manakau Harbour,* which Hochstetter classed as post-Tertiary in age. 
He also grouped the beds at Manakau Harbour with the terrace formation of the nnddle 
Waikato basin, of which the beds at Walton form a part. McKayf correlates the 
Tauranga Beds with similar beds in the valley of the Kauaeranga River and near 
Thames. These beds he classes as Newer Phocene and Pleistocene. FrascrJ adopts the 
same classification as far as the Kauaeranga Beds are concerned. 

Recent Dei'OSIts. 

Under this head are included various deposits differing somewhat in age. The 
deposits may be classified thus : — 

(a.) Piako Beds. 

(b.) Raised beaches. 

(c.) Dunes. 

{d.) Mud-banks and sand-bars. 

(e.) Gravels of the river-flats. 

(/.) Swamp deposits. 

(g.) Superficial pumice-deposits. 

(h.) Talus deposits. 

The Piako Beds. — These have a very extensive development in the subdivision. 
They cover large areas in the Waitoa, Aroha, and Wairere survey districts. They consist 
of interbedded gravels, pnmiceous sands, and silts loosely consoUdated. In general the 
sands are characteristic of the southern portion of the subdivision, and gradation to 
finer material is shown as the beds are followed northward towards the Hauraki Gulf. 
At Okauia, near Matamata, the lower portion of the sands is horizontally bedded, while 
the upper portion shows current bedding. A similar arrangement prevails in the few 
places where the beds may be examined, and it probably obtains throughout their whole 
extent. It is impossible to give an estimate of the thickness of these beds. Numerous 
bores have been put down in the Hauraki Plain in search of water ; but no logs were 
kept, nor would logs have been of much value, as the underlying Walton Beds closely 
resemble the Piako Beds and probably grade into them. As far as the writer could 
learn, the deepest bore, near Waitoa Railway -station, reached a depth of 1,200 ft. At 
this depth it penetrated more consoHdated sedimentary beds, apparently similar to those 
outcropping near Walton. 

Raised Beaches. — Raised beaches occur near Maukoro§ in the Waitoa Survey District, 
at Maunganui Mount, || and on Matakana Island. They may be correlated with the 



* Hochstetter, F. von : " New Zealand," 1867, pp. 62, 268. 

t McKay, A. : "Report on the Geology of the Cape Colvillo Poniii.siila," Mines Reports, 1897, 0.-9, 
p. 70. 

X Frasei-, C. : Bulletin No. 10, 1910, p. 29. 

§ Cnssen, L. : " On the Piako and Waikato River Basin.-;,'" 'I'lans., vol. .x.wiii, 189;!. p. 404. 

II Hutton, F. W. : " The Geological History of New Zealand," Trans., vol. xx.\ii, 1899, p. 179. 



78 

raised beaches at Orokawa* and at various other places ou the sea-border of the 
Hauraki Peninsula.! 

Sand-dunes. — These have extensive development along the eastern coast-hne, where 
they cover an area of about twenty-two square miles. 

Mud-banks and Sand-bars. — Tauranga Harbour has the greater portion of its area 
laid bare at low water. The maps do not show the distribution of these mud-banks 
except near each entrance, where Admiralty surveys have been made. 

River-gravels and Swamp Deposits. — These call for little comment in this place. The 
swamp deposits of the Piako have yielded moa-remains from time to time. Areas con- 
taining submerged kauri logs show where kauri groves once stood. 

Superficial Pumice-deposits. — These must at one time have covered a considerable 
area in the south-east of the Tauranga Survey District. Now, however, only small 
patches have escaped denudation. They are sandy deposits covering an older denuded 
surface upon which grew heavy vegetation. The writer regards them as of subaerial 
origin, and correlates them with similar deposits described by Gordon and McKayf as 
occurring in the Urewera country. 

Talus Deposits. — Talus deposits of considerable thickness are developed along the 
western scarp of Cape Colville Range from Waiorongomai to Okauia. 

The Hauraki Petrographical Province. 

Now that the whole Hauraki Peninsula has been subjected to a detailed geological 
examination, it may not be out of place to bring together the analyses made, from 
time to time, of volcanic rocks taken from widely separated points. The accom- 
pan3dng table, which includes analyses of comparatively unaltered rocks only, renders 
evident the consanguinity of the volcanic series. The whole suite may be considered to 
have been derived by differentiation from a magma, and to form a petrographical 
province of the Pacific type. A variation diagram has been prepared from the analyses 
after the method employed by Barker ; and for the sake of comparison the variation 
diagram§ of the suite of volcanic rocks from Lassen Peak, California, as representing a 
typical Pacific province, has been set beside it. When the difference in the sihca 
range of the rocks is considered, the similarity of these diagrams is remarkable. The 
curves for each basic radicle are of a like nature in the two diagrams. The chief 
difference lies in the relative position of the curves for the FejOg and CaO radicles. 

The study of other regions where a great variety of volcanic rocks has been 
extruded has shown that the first rock of the sequence is usually of intermediate 
composition — that is, in the case of a province of the Pacific type, an andesite — and 
that subsequent lavas are increasingly divergent from this rock. The Hauraki province 
shows an increasing acidity in three well-marked steps. Generally a sequence showing 
an increasing basicity is also developed, but in this instance it seems to be entirely 
suppressed. The rocks of the post-rhyohtic Dyke Series are of special interest, since 
they are of a hke composition to the initial andesites. It is difficult to conceive of 
their being a differentiation-product of the original magma ; and it is probable that they 
represent either part of a new magma or, if the original magma be regarded as an 
offshoot from a larger parent magma, part of the charge refilhng the old reservoir. The 
writer prefers the latter view, and has included the analyses of the dyke rocks in the 
accompanying table. 

* Bell, J. M., and Fraser. C. : Bulletin No. 15, p. 50. 

t Eraser, C, and Adams, J. H. :]_Bulletin, No. 4, p. 60. Fraser, C. : Bulletin No. 10, p. 29. 
t Gordon, H. A., and McKay, A.": " Exploration in the Urewera Country," Mines Reports, 1896, C.-3, 
p. 163. 

§ Taken from " Natural History of Igneous Rocks," 1909, p. 126. 



«» » »7 



^,0 




K2O 



A. Variation Diagram of Volcanic Rocks of Hauraki Peninsula from 32 Analyses. 



M,0 




45 50 55 60 65 70 75 80 

B. Variation Diagram of Volcanic Rocks from Lassen Peak, California, U.S.A. 

From "Natural History of Igneous Rocks," A. Harker, p. 126, London, 1909 (by 

permission of the Author). 



Geo. Bull. No. 16.] 



[To face p 79. 



79 





OS r-H 00 CO CO 

(N l- CTS l- p 

d> t^ rH CO O 

in I— 1 


CO rH '^ rH CO 

p c<j in op p 

CO CO rH C<1 O 


rH 
1 — 1 

6 


Nil 
1-46 
0-73 


1 — 1 

8 

I-H 

<M 




1 — 1 


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(ii i~ CO CO o 
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80 

1. Pyroxene andesite, Karaka Mines, Thames. Bull. No. 10, p. 24. 

2. Pyroxene andesite, Thames. Bull. No. 10, p. 24. 

3. Augite andesite, Maiden Mine, Opitonui. Bull. No. 4, p. 71. 

4. Hornblende dacite (? quartz andesite), Wiseman Gully, Thames. (ieol. Kep., 

vol. V, 1868-69, p. 40. 

5. Hypersthene andesite, Four-in-Hand Mine. Bull. No. 4, p. 70.' 
G. Hornblende-hypersthene andesite, Waihi. Bull. No. 15, p. 45. 

7. Pyroxene andesite, Kuranui Mine, Thames. Bull. No. 10, p. 24. 

8. Pyroxene andesite, Moanataiari adit, Thames. Bull. No. 10, p. 24. 

9. Hornblende andesite, Waikoromiko Creek. Bull. No. 4, p. 73. 

10. Quartz-biotite diorite, Moehau Range. Bull. No. 4, p. 90. 

11. Hornblende andesite. Halcyon Mine, Thames. Econ. GeoL, vol. iv, 1909, p. 637. 

12. Hypersthene andesite, Beeson Island. Bull. No. 4, p. 82. 

13. Hornblende dacite (? quartz andesite), Waihi. Econ. GeoL, vol. iv, 1909, p. 638. 

14. Pyroxene andesite, Waitoki-Mangakino Track. 

15. Hypersthene andesite, Sheehan's Creek. 

16. Hypersthene andesite, Wairakau Creek. 

17. Pyroxene andesite, Waimata Creek. 

18. Andesite, Long Bay. Bull. No. 4, p. 82. 

19. Hornblende andesite, Wairoa Stream (branch of Tuapiro). 

20. Pyroxene andesite, Romunga Creek, Waitawheta River. 

21. Hornblende-hypersthene andesite, Waihi. Bull. No. 15, p. 45. 

22. Quartz -hornblende andesite, Waitawheta River. 

23. Crystal tuff, Waitawheta River. 

24. Hornblende dacite (? quartz andesite), Waihi. Econ. GeoL, vol. iv, 1909, p. 638. 

25. Crystal tufi (dacite), Waiteariki Stream. 

26. Glassy dacite, Mangakino-Karangahake Track. 

27. Rhyohte tuff, Omoho Creek. Bull. No. 4, p. 64. 

28. Rhyohte tuff, " wilsonite, " Owharoa. 

29. Spheruhtic rhyolite, Purangi. Bull. No. 4, p. 87. 

30. Lithoidal rhyohte, Waihi. Q.J.G.S., vol. Iv, 1899, p. 467. 

31. Crumbly perhtic rhyolite, Waiau Stream. 

32. Spheruhtic rhyohte, Omahu. Q.J.G.S., vol. Iv, 1899, p. 467. 



Cause of Volcanic Eruptions. 

According to modern ideas, the formation and maintenance of intercrustal magmas 
is due to relief of pressure in connection with mountain-building or plateau-forming 
movements.* Since all the volcanic rocks must be regarded as the product by differen- 
tiation from a magma or group of magmas, it follows of necessity that the movement 
or series of movements which brought about the existence of the magma or group of 
magmas must have been of great magnitude and persistence. The manifestations of 
volcanic energy were on so vast a scale that the only movement competent to have 
produced them is that which caused the foundering of the Hauraki grdben and the 
elevation of the Cape Colville Range. This was a movement of the plateau-forming 
order, which has without doubt been active since Pliocene times. f The fact that 
the -volcanic rocks in the Coromandel Subdivision rest upon the denuded fragments 
of sediments probably of Miocene age fixes with sufficient accuracy the time of the 



* Harker, A. : " Natural History of Igneous Rocks," 1909, p. 12. 
t See page 52. 



81 

commencement of this great movement, and brings it into line with the great radial 
movements which have afEected the Miocene rocks oi the South Island — in Otago,* 
Westland,t and Nelson.J 

Within the Aroha Subdivision the rooks upon which the andesites rest are exposed 
only in the Hangawera Hills. Here the volcanic rocks overhe with great unconformity 
sharply folded argilhtes and grauwackes. In the Coromandel Subdivision remnants of a 
subaqueous terrain, part of the main coal-measures of New Zealand, are interposed 
between the volcanic rocks and the grauwackes. These Tertiary rocks are extensively 
developed at Huntly and Miranda, to the west. of the Hauraki (jrahen, and also in the 
Urewera country. On its emergence from the sea the Cape Colville earth-block was 
mantled by the coal-measures, which were, however, probably nearly all removed by 
denudation before the extravasation of Ihe lavas. If the assumption that the mani- 
festations of volcanic energy were caused by and were therefore later than the crustal 
movement of which the foundering of the Hauraki grdben forms a part, be correct, 
if may be asserted with some confidence that coal-measures underhe, at an unknown 
but great depth, the Hauraki Plain. 

The Extent and Nature of the Andesitic Accumulations. 

The great accumulation of volcanic rocks of intermediate composition, which forms 
the lowest portion of the Cape Colville Range within the subdivision, extends northward 
at least as far as the Great Barrier Island. Park§ considers that the andesites of 
Whangaroa Heads form part of the same volcanic suite. To the southward their 
extension is unknown, but the propyhtized andesite of Te Puke may safely be correlated 
with them. In the Hangawera Hills, to the west of the Hauraki grdben, a pyroxene 
andesite occurs which cannot be distinguished from similar rocks from the Cape Col- 
ville Range. The writer regards the andesites of the Cape Colville Range as only a 
portion of a once much more extensive area of similar rocks. Park]] points out the 
great abundance of flow andesites when compared with fragmental rocks of a like 
composition. Bell and Fraser^[ in the Waihi-T^airua, and the present writer in the 
Aroha, Subdivision have noted a similar condition. The andesitic eruptions probably 
approached the fissure type, a suggestion which finds support in the fact that the 
crustal movements which caused the extravasation of the lavas were of the plateau- 
forming order which are associated with the fissure eruptions.** Since the foundering of 
the Hauraki earth-block not only caused the outpourings of lava, but also produced 
the fissures from which the molten streams welled, it is probable that the fissures had 
a strike parallel to the trend of the (jrahen — that is, a httle to the west of north. 
This agrees with the general strike of the folded sediments forming the plinth of the 
Cape Colville Range. 

Period op Propylitization. 

Fraser and Adamsff refer the veins of the Coromandel Subdivision to two periods 
of minerahzation. Fraser"|{ considers the veins of the Thames Subdivision to be due 
to three more or less distinct periods, and a similar conclusion is reached by Bell and 

* Park, J. : " Geology of New Zealand," 1910, p. 144. 
t BuUetin No. 6, 1908, p. 37. 
X Bulletin No. 13, 1912, p. 44. 

§ Park, J. : " Geology of New Zealand," 1910, p. 154. 

II Park, J. : " Geology of New Zealand." 1910, p. 341. In Bulletin No. 4, 1907, p. (>."). the contrary is 
stated for the Coromandel Subdivision. 
If Bulletin No. 15, 1912, p. 27. 

** Harker, A. : " Natural History of Igneous Rooks," 1909, p. 40. 
tt Bulletin No. 4, 1907, p. 98. 
XX Bulletin No. 10, 1910, p. 33. 

6 — Aroha. 



82 

Fraser* in regard to the veins of the Waihi-Tairua Subdivision. As far as the lodes 
of the Aroha Subdivision are concerned, there is no necessity to postulate more than 
a single period of propyUtization, which would be after the emission of the dacites and 
dacitic crystal tuffs and before or perhaps contemporaneous with the deposition of the 
rocks of the Mudstone Series. Since the fissured zones from which propyHtization 
proceeded strike generally north-eastward, it may be assumed that these fissures were 
at that time the most active. Perhaps even the vents from which the dacitic rocks 
were emitted were distributed along hnes with a north-east strike. 

Correlation of the Rhyolites and Post-Rhyolitic Dykes, 

In 1897 Parkf correlated the rhyoHtes of Hauraki Peninsula with those of the 
central portion of the North Island. The work in the Aroha Subdivision has shown 
that the Hauraki rhyoUtes may be traced at least as far south as Tauranga. The 
beds of pumice-sands developed in the upper portions of the Tauranga Series, which 
are undoubtedly younger than the Hauraki rhyohtes, may have been derived from 
previously existing pumice-deposits or from eruptions of rhyoUtic matter proceeding 
contemporaneously in some locahty beyond the hmits of the district examined. It 
is tempting to consider the igneous rocks of the Hauraki Peninsula and of the " Taupo 
Zone " as forming each a part of the same volcanic province. If this be so, the 
post-rhyoHtic andesite dykes of the Aroha Subdivision may be correlated with the 
andesites of the numerous cones rising from the rhyolitic plateau of the North Island. 

Geological History. 

Probably the area now treated of as the Aroha Subdivision was dry land 
immediately prior to Miocene time. Then submergence permitted the accumulation of 
marine beds, which, however, nowhere outcrop within the area dealt with. Crustal 
stresses found rehef in the formation of great meridionally disposed fissures, in the 
differential elevation of the earth-blocks between these fissures, and by the outpouring 
of vast floods of andesite from them. The initiation of the Hauraki rift-valley belongs 
to this period, and its floor was, probably covered by the lavas. The movements were 
intermittent, and spread over a considerable time-interval, but finally a temporary 
adjustment of the forces allowed the volcanic manifestations to become dormant. 

Again, earth-movements affected the area, and rocks of a dacitic composition were 
emitted. Later these and the underlying andesites were riven by north-east striking 
fractures, and heated solutions, arising along the fissured zones, propyhtized great masses 
of rock. At this time the greater part of the area at present occupied by the 
Ohinemuri basin must have been a shallow lake, around the margin of which swamps 
flourished, while on the floor gravels, sands, and muds were laid down, the material 
being derived from the still active craters which later entirely filled in the lake-basin 
with breccia. 

A period of denudation followed, and at this time the land as a whole stood at a 
higher elevation than at present, and the drainage system was altogether different from 
that of modern times. 

Little can be said concerning the emission of the rhyohtic rocks. It is known 
that during or towards the close of this volcanic period depression took place, and the 
valley of the Ohinemuri was filled in and the river diverted to the Hauraki Gulf. 
The Tauranga Beds were laid down, the material being probably derived from a large 

* Bulletin No. 15, 1912, p. 52. 

t Park, J. : " Geology and Veins of the Hauraki Goldfields," Trans. N.Z. Inst. Min. Eng., vol. i, 1897, 
p. 37. 



83 

river flowing from the centre of the North Island. The Walton Beds have a similar 
origin. This was a period of stillstand as far as the area represented by the Aroha 
Subdivision is concerned. Denuding agents acting on a low-lying land produced a 
mature topography. 

Movements probably connected with the intrusion of the dykes brought this period 
to a close. In the area described the dykes follow an east-and-west course, but other 
post-rhyoUtic dykes occurring in the Hauraki Peninsula strike north-and-south. The 
principal movements were along the reopened ancient fissure-zones, and especially along 
the great fractures determining the Hauraki grdben. It is to the differential elevation 
of the earth-blocks at this period that the present configuration is due. On the 
whole, the Cape Colville earth-block was elevated within the Aroha Subdivision more 
on the western side than the eastern, while the small blocks comprising the range were 
individually tilted to the north. 

After land -sculpture, depression caused the drowning of the lower courses of the 
streams on the eastern side, and the smothering by swamps of the kauri forests at 
that time growing on the Piako Plain. The latest movement has been one of elevation, 
as evidenced by the raised beaches at Tauranga, Matakana Island, and Orokawa, on the 
Bay of Plenty, and by the shell-banks at Maukoro and near Waitoa, and in general by 
the entrenching of the Waihou in the plain. 



*** — Aroha. 



84 



CHAPTER VII. 



ECONOMIC GEOLOGY. 



Karangahake Mining-avea 


Page 
84 


Facts observed in connection with 


the 


Physiography 


84 


Ore-deposits — continued. 




Faulting . . 


84 


Influence of Faiilts, &c. 




Lode Fissures 


85 


Influence of Present Topography 




Propylitizatiou 


86 


Nature of Country 




Weathering 


87 


Nature of Mine- waters 




Te Aroha Mining-area 


88 


Physico-chemical Data 




Physiography and Faulting . . , 


88 


Summary 




Lode Fissures 


88 


Genesis of the Ore 




Owharoa Mining-area 


89 


Introduction 




Waitakohe Mining-area 


89 


Ascension Theory . . 




Lode Minerals 


89 


Secondary Enrichment Theory 




Facts observed in connection with the 




Lateral Secretion Theory 




Ore-deposits . . 


92 


Conclusion 




Propylitization 


92 


Future Prospects 




Persistence of Lodes in Depth 


93 


Karangahake 




Gangue . . 


94 


Te Aroha 




Distribution of Metallic Contents of 




Waitakohe 




Lodes . . 


94 







Page 



97 
98 
99 
100 
101 
102 
102 
102 
103 
104 
107 
108 
108 
109 
109 



Karangahake Mining-area 

Physiography. 

The Karangahake mining-area is practically co-extensive with the Karangahake 
mountain-mass. The physiography of this has been mentioned under a previous chapter, 
but will here be described in more detail. 

The mountain-ridge, 70 chains in length, runs in a north-east direction, and rises 
from 1,500 ft. to a little over 1,800 ft. above sea-level. On the north-west flank there 
is abrupt descent to a long ridge which stretches towards Paeroa. On the south-east 
the descent is directly to the deep valley of the Orima. The ridge at its northern 
end terminates in a sharp semi-detached peak 1,755 ft. in height — a landmark for many 
miles. This peak drops precipitously to the profound gorge of the Waitawheta, 1,600 ft. 
below. A thousand feet from the summit is a remnant of the valley-floor of the ancient 
Ohinemuri River. This valley-floor is continued across the Waitawheta in Taukani Hill 
(820 ft.), and thence across the Ohinemuri to the Rahu Saddle. 

Faulting. 

It is beheved that the topography just described is mainly due to the fact that the 
Karangahake Ridge is a block mountain. On the north-west flank of the mountain runs 
the Romani-Karangahake Fault, really a sheeted zone which manifests itself in the 
wide belt of crushed rock on the saddle between Karangahake and Rotokohu, and again 
near the Crown Mill at Karangahake. On the south-east side of the mountain the 
Orima has cut its valley along the Waitoki-Orima Fault, which causes the crushing at 
the mouth of the Orima and in the Waitawheta and Ohinemuri valleys. A subordinate 
system of faulting runs west-north-west along the northern end of the mountain block. 
Several of the faults of this system have been exposed in mining operations, but none 
so far have been of great magnitude. The " Clay Bank " of Taukani Hill also belongs 
to this system. These faults, in combination with an extension of some of the lode 
fissures, seem to have determined the peculiar bendings of the Ohinemuri and Waita- 
wheta rivers in their respective gorges. 





Diagram of Lode Fissures 
Karangahake Mining Area 



Scale of Chains 



I ' I '_' I J I I ' I 



:3= 



q-U 



Geo. Bull. No. 16.1 



[To face p 85. 



85 

Lode Fissures. 

The most persistent lode fissure of the area is that occupied by the Maria reef. 
Starting from the north as the Sir Walter Scott reef this fissure has been explored 
for a total length of nearly 100 chains. The northern portion strikes between north- 
north-east and north-east, then for 15 chains the strike is a little west of north, next 
for about 10 chains the strike is again north-east, while for the last 20 chains in the 
south the strike is nearly north-and-south. It is believed that the fissure occupied by 
the Maria lode is composite, being formed of two sets of fissures — one set striking 
north-east and the other nearly north. 

A similar arrangement seems to prevail in respect to the Welcome lode— 12 chains 
to the east of the Mai'ia — the northern portion of which strikes north, and the southern 
portion north-east. Moreover, there is a tendency for this fissure to turn north- 
east again at the northern Umit of exploration, and to turn south at the southern 
end. 

The only other fissure sufficiently explored to yield information on this point is the 
new lode of the Crown Mines, now usually known as the Crown lode. This, in its 
northern portion, strikes north, changing to north-east in the southern portion. 

As far as known, the other lodes of the district also conform to these two directions, 
those striking north-east being the commoner. 

The distribution of the lode fissures is shown in the accompanying sketch-plan, 
while most of the mine-workings are shown on Map 7. It must not be supposed, 
however, that all the lodes are here shown. Innumerable stringers of quartz occur in 
the upper portion of the mountain, and in every drift crossing the general trend of 
the lodes many vein lets of quartz or calcite are found. 

In regard to the relative age of the lodes nothing absolute can be said. In the 
unoxidized portion of the Maria lode, where the fissure is striking north, numerous small 
stringers with a north-east strike join in on the hanging-wall ; similar stringers do not 
seem at this place to leave the foot-wall of the lode. This suggests that the north- 
striking fissures are older than the north-east fissures. Such observations confined to 
a limited portion of one lode are of httle value : but in the Te Aroha mining-area, 
a few miles to the south, there is evidence that north-east striking fissures have cut a 
north-striking fissure-zone. 

The north-east striking fissures, which are the dominant fissures of the district, are 
certainly connected with the north-east Lfaults of the area, and were formed by the 
stresses which produced the other north-east striking fractures of the Aroha Subdivision. 
The lode fissures must be regarded as fissures in a sheeted fracture-zone. Crushed 
pug - bands and fault - breccias, independent of later faults, are common in all the 
fissures which have been extensively explored. It is believed that the movement along 
any particular fissure has been small, although, save in the case of the Maria, it is 
impossible to prove this statement. In the Maria fissure, in No. 13 level, a band of 
fine-bedded tuff is exposed on both walls, and the total relative movement of the walls 
cannot have been more than a few feet. Ore-deposition does not seem to have taken 
place in the fractures of large movement, nor does there seem to have been movement 
along the fissures after the deposition of the ore. This statement does not apply to 
the western reef of the Dominion Lease, which has been crushed along its length by a 
fault belonging to the Romani-Karangahake crush-zone. 

The dip of the lode fissures is westward, although in parts of the Maria fissure the 
dip is vertical, or even to the east. The dips of the principal lodes are shown on 
Sheet 9. 



86 

Propylitization. 

The geology of the Karangahake mining-area has akeady been described, but the 
sequence of the beds may here be recapitulated. As exposed in the Tahsman Mine, 
the succession in ascending order is : — 

(a.) Andesite. 

(6.) Breccia with slate fragments. 

(c.) Andesitic tuff. 

(d.) Breccia with andesite fragments only. 

(e.) Augite-hypersthene andesite. 

(/.) Spherulitic dacite. 

Of these it is beheved that the first five beds belong to one series, and that the 
last was extruded upon this series only after a considerable time -interval. All 
the rocks have been subjected to such alteration by heated ascending and cold oxidizing 
descending solutions that on the surface it has been found impossible to map the 
boundary of the two series exactly, while underground observations touching this point 
could not be made, as all workings except those in the Andesite Series are now closed. 
The plans and sections of the Tahsman Mine, however, show that the Maria fissure 
was continued into the overlying dacite. 

Two phases of propylitization may be recognized — the first, in which the ferro- 
magnesian minerals are altered to chlorite, serpentine, &c., and the second, in which 
the feldspars and iron-ores are also attacked. These phases are not sharply separable, 
but grade into each other. 

The first stage of the alteration seems to be the alteration of the rhombic pyroxenes 
to a mixture of chloritic and serpentinous material with formation of some sericite. 
These alterations imply a certain interchange of molecules between the ferro-magnesian 
minerals and the feldspars, as also does the alteration of the hypersthene to a mineral 
resembhng urahte. The augite crystals at this stage are quite unaltered, but the 
feldspar often shows a development of chloritic mineral along the cleavage-planes. 
Probably, however, the principal portion fii the lime required in this alteration is 
obtained from the glassy basis, which alters to a mosaic of quartz grains. This, the 
first stage of propyhtization, is very widespread, and some writers* apparently consider 
that the sUghtly altered rock of this stage is a separate species. The writer does not 
intend to discuss this threadbare question. As far as the evidence yielded by the 
work in the Aroha Subdivision is concerned, there is no justification for this view, or 
for that advanced by Finlayson — " that the chloritisation took place immediately after 
the eruption of the rocks and during their solidification, through the agency of contained 
solutions or gases rich in carbon-dioxide, which is such a characteristic product of 
volcanic action. "f 

In the next stage the augites are attacked. They seem to alter to chlorite, 
epidote, and calcite with hberation of quartz. An intermediate uralitic stage has also 
been noted. This alteration does not require the local migration of the bases needed 
in the alteration of hypersthene. Such migration, however, probably takes place during 
the complete transformation to chlorite, which occurs at this stage, of the serpentinous 
alteration-product of the hypersthene. 



* Sollas, W. J. : " Rocks of the Cape Colville Peninsula," vol. i, 1905, p. 120. 

t Finlayson, A. M. : " Problems in the Geology of the Hauraki Goldfield."^cono»ntc Geology, vol. iV' 
1909, p. 640. 



87 

The second phase of propylitization is called the " sericitic phase " by Kirk.* The 
hrst stage of this phase of the alteration seems to be the conversion of the feldspars 
into a mixture of sericite, calcite, and quartz. Epidote is entirely destroyed, chlorite, 
calcite, and quartz being formed. Some molecular migration evidently takes place, 
since chlorite often replaces feldspar in part. The iron-ores are converted to siderite, 
and if titanium is present leucoxene forms. 

In the last stage of alteration the chlorite and siderite seem to be converted to 
pyrite. This involves the introduction of sulphur, probably as sulphuretted hydrogen. 
At this stage also iron seems to have been introduced, for more pyrite is present 
generally than could arise from the conversion to pyrite of the total original iron-content 
of the rock. The pyrite is often present in fine grains, marking the outhne of an 
original ferro-magnesian mineral. 

The final result of propylitization is the conversion of the rock to a fine-grained 
whitish mixture of quartz, sericite, and calcite, with a variable content of disseminated 
pyrite. This complete alteration only obtains quite close to the fissure from which 
propyHtization proceeded. The bulk of the rock, even in intensely propyhtized areas 
of andesite, has a greyish-green colour, due to the presence of incompletely destroyed 
chlorite. In the case of the dacitic rocks, the propyHtization of which may be studied 
at Owharoa, changes similar to those enumerated for the andesites have been observed. 
In these rocks traces of spheruhtic structure have been preserved to the last. The 
alteration of the andesitic breccias and tuffs of the Karangahake area is of the same 
character as that of the andesites, except that the fine-grained tuffs seem to have 
resisted the propylitizing agents better than the andesites. 

Weathering. 

In the process of propylitization as just described it will be noted that the ferro- 
magnesian minerals were first attacked. In normal atmospheric weathering they resist 
attack much better than the feldspars, which are usually the first minerals to alter. 

The active agents in normal weathering are the gases dissolved in the downward- 
percolating meteoric waters. The feldspars are attacked by carbonic acid, with formation 
of kaoHnite, hberation of siUcic acid, and solution of the alkahes and 'alkaUne earths as 
carbonates. These latter, together with part of the sihcic acid, are removed from the 
place of formation, and either deposited elsewhere or carried to the surface by the 
meteoric waters. The ferro-magnesian minerals, when they do weather, yield soluble 
bicarbonates of magnesium, iron, and calcium. Much of the iron, however, is converted 
to insoluble hydrates. The final result of weathering upon andesite is the conversion 
of the rock to a ferruginous clay. 

The weathering of propyhte presents somewhat different features. Here the rocks 
are mainly a mixture of quartz, sericite, calcite, and other carbonates, with a variable 
admixture of pyrite. There is always in the rock-mass portions of the rock which have 
not reached the final stage of propylitization, and which contain chlorite and other 
constituents of the original rock. All writers agree that propyhte is very much more 
susceptible to weathering agents than is the unaltered rock. Of the constituent minerals 
calcite is the first to be removed. Oxidation of the pyrite yields sulphuric acid, and 
the sericite readily yields to this powerful acid with the formation of kaoUnite and 
liberation of potassium and aluminium sulphates and silicic acid. Part of the dissolved 
substances is redeposited at a lower level as calcite and quartz. The surface rock is 
ultimately converted to a porous mass of quartz and kaolinite, the whole stained with 
iron-hydrates. 

* Kirk, C. T. : " Conditions of Mineraliiiation in the Copper-mines of Butte, Montana," Economic Geology, 
vol. vii, 1912, p. 52. 



88 

Te Aroha Mining- area. 
Physiografhy and Faulting. 

The Te Aroha inining-area is confined to the Te Aroha mountaiu-niass. This, 
the highest peak of the whole H^uraki Peninsula, attains its full height of 3,126 ft. at a 
distance of only 120 chains from the level Hauraki Plain. The outcrops on the track 
from the town to the trigonometrical station seem to suggest that the mountain is 
composed of alternate layers of rock, while the profile of the mountain as viewed from 
the north shows a step-like arrangement. The "tread" of each step is composed of 
breccias and flow rocks belonging to the Dacite Series, while the " rise " consists of rocks 
of the Andesite Series. Cox, who examined the area in 1882, noted the apparent alter- 
nate banding of dark and light coloured rock, and considered the mountain to be built 
up of such alternate layers.* The present writer beheves the arrangement to be due to 
step-faulting. That the scarp of a great fault forms the south-south-west face of the 
mountain has already been noted. A fault parallel and subsidiary to this separates Bald 
Spur from the rest of the mountain. This fault may be seen in the Tutumangao 
Creek, where a vertical junction between the two series of rocks occurs ; south of Bald 
Spur the low hills buttressed along the foot of the mountain -scarp mark the course of 
the fault which also dislocates the Buck Reef, as wel' as producing the '' shp country " 
in which the original discovery of gold at Te Aroha was made. The next fault-step is 
separated from the main peak of Te Aroha by the saddle between the Tutumangao and 
Stoney Creek. Although no positive evidence as to the existence of this fault was 
observed, the topography of the mountain and the distribution of the rocks strongly 
suggest its occurrence. 

The fault striking north-north-east between Te Aroha and Puketutai mountains 
and that following the course of the Waiorongomai have already been mentioned. 
Extensive crushing may be noticed along the track encirchng the head of the Mangakino 
Stream, but no evidence definitely fixing the strike of the fault could be obtained. 

The writer, then, regards Te Aroha Mountain as essentially a block mountain. 
Hochstetter,! who did not actually visit the mountain, shows it on his map as a 
trachytic cone ; ParkJ seems also to regard it as a volcano. 

Lode Fissures. 
The lode fissures of the Te Aroha mining-area are exceedingly numerous. The 
largest lode of the subdivision and also of the Hauraki Peninsula — the Waiorongomai 
Buck Reef — has been traced a distance of 240 chains, and occupies a crush-zone 
striking nearly north-and-south. As far as the writer could observe, the dip was to the 
east, at a very steep angle, and this is certainly the dip at the southern end ; but 
reliable mining men report that its dip is to the westward in the New Find workings. 
The " reef " consists of a zone of crushed and silicified country of variable width, 
traversed by numerous longitudinal and obhquely transverse quartz stringers. The 
figures given below must be considered only approximate, since the sihcified rock 
generally merges gradually into the country. On the other hand, in some places a pug 
band sharply marks the boundary. At the southern end this great zone is about 60 ft. 
in width ; 35 chains from the southern end a crosscut shows a width of between 
90 ft. and 100 ft. At Diamond Gully it is about 140 ft. wide, while at the crossing of the 
Premier Stream it may be 30 ft. At the northern end the sihcification is not so 
intense, and the quartz stringers are rare. Its width here, in the head of the Manga- 
kino, is uncertain, but must be considerable. Throughout the whole of its length, except 



* Cox, S. H. : Geological Survey Reports, vol. xv, 1883, p. 15. 

t Hochstetter, F. von : " New Zealand," 1867. 

f Park, J. : " Geology of New Zealand," 1910, p. 153. 



Plate IX. 




Te Aroha Do?.rAiN. - Bald Spur in Background. 




Soi TiiKRN Portion of Hi cue K'kkk, ^VAIOR()N^;()^r.\I. 



Geo. Bull. Xo. ir,.-\ 



\_To fare p. SS. 



4 .^^^ 




Diagram of Lode Fiasures 
T©Arpha Mining Area 



m o 

llllll1-IUI-1»^'~^^ 



Scale of Chains 

40 



(^■e4 



Geo. Bull. No. 16.] 



[To face p. 89. 



89 

on the saddle between the Premier and Mangakino streams, the lode is readily traceable. 
A.t many places along this hne it stands up hke a great wall, sometimes over 200 ft. 
high, but at the northern end it is evidently softer than the surrounding country, for 
the Mangakino has cut its channel along the belt for many chains. That fault-move- 
ments have occurred along this zone is unquestionable, for pug bands and friction 
breccias are found in places, and, moreover, the eastern wall differs from the western, 
often consisting of rocks similar to those of the Dacite Series. This is, however, by 
no means certain, as propylitization has obscured the characteristics of the country. 

From time to time this great siUcified zone has been thoroughly sampled, and has 
been proved to carry a little gold and silver, usually only in traces. It carries payable 
ore only where joined by some other reef. 

In another place it has been mentioned that almost all the Te Aroha lodes strike 
north-east, and occur in a zone of sheeted country. These lodes join the Buck Reef, 
and penetrate into its mass, but seem neither to cross it nor to continue as strong 
lodes upon the other side. Sometimes a north-east striking lode on reaching the 
Buck Reef changes its course, and follows one or other of its walls, ultimately pene- 
trating into the sihcified zone. 

The large lode which runs in a north-east direction through the northern portion 
of this mining district has been worked at various points in the Montezuma, Ishngton, 
Tui, and Mikado claims. It is only in the Tui Claim, however, that ore-bodies of suffi- 
cient value to justify exploitation have occurred. This great lode is similar to the 
Buck Reef, and consists of a zone of silicified country. Smaller lodes cross the main 
zone, or run longitudinally with it. The sketch-plan shows the distribution of the lodes 
of the Te Aroha mining-area. 

As far as the writer's observations go,^and as far as he could learn, the dip of all 
the veins is consistently to the west and north-west, with the single exception of the 
big lode. 

The Owhaboa Mining-area. 

Only the southern portion of this area is within the Aroha Subdivision. This small 
portion lies between the Ohinemuri and Waitawheta rivers. The topography when com- 
pared with that of the Karangahake and Te Aroha areas is relatively subdued, the spur 
between the rivers having been cut from the floor of the old Ohinemuri Valley. The 
lodes, of which three groups exist, strike north-north-east and north through pro- 
pylitized spheruhtic dacite. For further information concerning this area see Bulletin 
No. 15 (New Series), page 117. 

Waitakohe Mining-area. 

This area of propyUtized rock hes in the valley of the Waitakohe Stream. The 
lodes occur mainly in the steep ridge to the north of the creek, but propyUtized rock 
forms the southern side of the valley, and reaches nearly to the saddle of Thompson's 
Track, which is crossed by several silicified zones of rock. Only one lode — the Eliza — 
has been prospected, and so far this has not given satisfactory results. 

Lode Minerals. 

Qtiartz. — This is by far the commonest lode mineral, forming as it does the principal 
gangue-mineral of the ores. Much of it is cryptocrystalhne, and this variety has in 
part been formed by silicification of wall-rock, of brecciated fragments of wall-rock, or of 
pug. Coarsely crystalhne transparent quartz with well-developed crystal faces occurs 
in portions of the lodes. Sometimes the vein-material is beautifully banded, yellowish 
chalcedonic layers alternating with crusts of radially crystallized transparent quartz. 
Sometimes cellular liackly quartz occurs. This is after calcite, and all the stages of the 



80 



replacement may be studied. The attack of the sihceous solutions is not altogether 
peripheral. Cleavage-planes and irregular fractures are taken advantage of, and when 
the calcite has all been removed the quartz remains as fragile septa covered with 
small quartz crystals. Sometimes quartz replaces the calcite entirely, and then each 
cleavage-flake of calcite is represented by closely packed, evenly sized quartz grains, 
each grain terminating against the cleavage-plane with a flat surface. Quartz, probably 
pseudomorphous after aragonite, was observed in connection with the Vulcan lode 
at Waiorongomai. Opaline quartz, common opal, and occasionally precious opal occur 
as a result of meteoric weathering in connection with rhyohtes and dacites near 
Waikino, and with dacite tuffs a Uttle south of the Waiteariki Stream. Hyahte is 
mentioned by Pond* as occurring at Karangahake. 

Calcite. — Calcite is a common gangue-mineral only in the unoxidized lodes or 
portions of lodes. It occurs thus in the Bonanza section of the Maria lode. Again, 
in unoxidized propyhte every Uttle fissure is filled with calcite. It is occasionally 
found crystalline as a late deposition on comby quartz or on oxidized ore. 

Ankerite. — This carbonate of iron, magnesia, and hme, although not nearly so 
common as calcite, has a similar distribution. 

Rhodochrosite. — It is believed that most of the calcite occurring in the lodes contains 
more or less manganese-carbonate. Rhodochrosite occurs in bands in the unoxidized 
portion of the Bonanza shoot, Tahsman Mine. 

Wad. — The rhodochrosite of the unoxidized ore is represented by the wad of the 
oxidized ore. Under this name are included various earthy, impure, hydrous oxides 
of manganese, which are not crystalline, and have no definite chemical composition. 
Wad seems to be particularly common in connection with platy quartz. The nickel 
and cobalt reported by AUenf as occurring in the Woodstock Claim (Maria lode) are 
probably contained in the wad. 

Valencianite. — This feldspar, since it has been found with calcite and quartz in the 
unoxidized lode stuff, may also be considered a gangue-mineral. It is also found in 
the country. 

Epsomite. — Epsomite occurs in long silky tufts as an efflorescence on the walls of 
old warm drives. 

Melanterite. — Melanterite has also been observed in old workings, but does not 
seem to be as common at Karangahake and Te Aroha as at Thames. 

Mirahilite. — The hydrous sulphate of soda has not been observed in crystalline 
form, but sodium-sulphate occurs in the mine-waters. 

Alunite. — Alunite was not observed, but aluminium is present in the mine-waters 
and in the TaUsman ores. 

Kaolinite. — KaoHnite occurs abundantly in the oxidized country, but is not so 
conmion at deeper levels. 

Halloysite. — Halloysite from the Hauraki Mine (Tahsman) was analysed by SkeyJ 
with the following result : — 

Sihca .. .. .. .. .. .. .. 4541 



Al.Og 


.. 28-64 


Fe oxides . . 


. . . . . . Traces. 


CaO 


.. 1-62 


MgO .. 


.. 0-11 


HjO 


.. 24-22 




100-00 



* Pond, J. A. : Mines Reports, 1887, p. 58. 

t Allen, F. B. : New Zealand Mines Record, vol. iv, 1901, p. 469. 

+ Skey, W, : Colonial Laboratory : 19th Annual Report, 1885, p. 29. 



91 

Platinum. — This metal is reported by H^eusler as occurring in a boulder near 
Owharoa. 

Oold. — Gold occurs either as alluvial or in lodes. Alluvial gold is found as a 
shedding from the lodes. It has been commercially worked at Owharoa and in the 
" Shotover basin " (Rotokohu-Karangahake Saddle). It is really an electrum. The 
gold of the reefs is also electrum, and the fineness ranges from 645 to 850. The 
fineness of the gold may alter very suddenly. Thus in a small branch vein of the 
Maria lode the fineness was nearly 900, while in the Maria itself the electrum is about 
650 fine. The variation of gold and silver in the electrum is a characteristic of both 
the Karangahake and Te Aroha mining-areas, but owing to the available data being 
unrehable no exact figures can be given. 

Silver. — Silver in the native state is not of common occurrence. The only occurrence 
seen by the writer was in No. 13 level of the Bonanza section of the Tahsman, 
where beautiful specimens of wire silver have been obtained. It has been reported also 
from the higher levels. 

Hessite.— As early as 1885 Skey* detected tellurium in a sample of ore from Kara- 
ngahake. As the specimen contained only a trace of gold and large quantities of silver 
he assumed the occurrence of a telluride of' silver.. Tellurium is also reported from the 
Moaf and Tui mines, Te Aroha, and the. writer was shown a specimen from the Premier 
Claim. 

Argentite. — This is the commonest of the silver minerals. It is found in almost 
all the mines and prospects of the subdivision. It is usually distributed in very fine 
grains, or as streaks and patches in the quartzose ore. 

Kerargyrite. — The chloride of silver has been reported from the upper levels on 
the Maria lode in the Woodstock section of the Talisman Mine. SkeyJ in 1887 
mentions the occurrence of kerargyrite in the Te Aroha ores. The writer observed a 
specimen in rich ore from No. 11 level, Tahsman Mine. 

Bromargyrite. — This mineral was detected from below the outcrop of the Maria 
lode in the Woodstock Claim by R. B. McDuff. 

lodargyrite. — The iodide of silver was reported by SkeyJ from Te Aroha. The 
assayer of the Bank of New Zealand at Paeroa§ reported the presence of iodine in the 
bulhon from the Woodstock Claim, Karangahake. 

Mercury. — This metal was identified by Hseuslery from the river-gravels at Owharoa. 

Amalgam. — Is also mentioned as occurring at Owharoa. || 

Cinnabar. — Cinnabar was identified from Te Aroha by Skey J in 1887. It also 
occurs in the mineralized ore of the Tui Mine ; and a specimen from this locality, 
collected by P. G. Morgan, is in the Waihi School of Mines. It occurs in alluvial deposits 
at Owharoa. In this locahty mercury minerals and p]atinum|| are present in a river- 
wash, and it has not been possible to refer any of these minerals to an immediate 
source. Probably they come from the Tui deposit at Te Aroha. 

Pyrite. — This is exceedingly common. It occurs in all lodes which have not been 
too long subject to oxidation. All the andesites of the subdivision contain it to 
a greater or less extent, and in the altered rocks forming the country of the lodes 
it is always present in considerable quantities. 



* Skey, W. : Colonial Laboratory : 19th Annual Report, 1885, p. 37. 

t Cox, S. H. : " On the Occun-ence of some New Minerals in New Zealand," Trans., vol. xvi, 1883, 
p. 449. 

t-Skey, W. : Colonial Museum and Laboratory : 22nd Annual Report, 1887, p. 56. 

§ Mines Reports, 1889, C.-2, p. 21. 

II Haeusler, R. : " On the Microscopic Structure of the Ohinemuri Gold," Trans., vol. xxiii, 1890, 
pp. 335-40. 



92 

Mareasite. — This mineral is not nearly so plentiful as pyrite. It occurs in the 
oxidized portions of the lodes. 

Magnetic Pyrites. — This mineral is mentioned by Pond* as occurring at Te Aroha. 

Limonite. — This and other oxides of iron occur in the oxidized portion of rocks 
and lodes. All stages of oxidation between pyrite and Umonite have been observed. 
Black sooty sulphurets occur in many places — e.g., in the Woodstock section of the Maria 
lode. 

Chalcopyrite. — This mineral has been observed in the Maria and Welcome lodes at 
Karangahake, and seems to be present to a much greater extent in the Te Aroha lodes. 

Bornite. — Erubescent sheens point to the occasional presence of bornite. 

Govellite. — This mineral occurs in connection with exceedingly rich ore in the stopes 
of No. 12 level, Bonanza section, Maria lode. It is also reported from Te Aroha. 

Malachite and Azurite. — These hydrous carbonates of copper are present wherever the 
chalcopyrite has been oxidized. 

Dio'ptase. — A green coating on dxusy quartz from the Welcome lode has been 
referred to this mineral. 

Galena. — This mineral occurred in large masses in the Tui Mine, and is frequent 
in all the Te Aroha lodes. Pondf assayed galena from Waiorongomai, and found it 
to contain per ton : Silver, 3 oz. 8 dwt. 14 gr. ;■ gold, 9 dwt. 19 gr. From galena from 
the Tui district he obtained — Silver, 9 oz. 2 dwt. 22 gr. and 26 oz. 12 dwt. 11 gr. ; for 
gold, trace and 3 dwt. 6 gr. It is not so common at Karangahake. 

Gerussite. — According to ParkJ large quantities of cerussite were taken from the 
Tui lode. - A small specimen of this mineral was found in Comes' reef, No. 12 level, 
Talisman. 

Anglesite. — Is also mentioned by Park. J 

Grocoite. — Pond* identified this mineral in lodestufE from Waiorongomai. The identi- 
fication is doubtfuUy correct. 

Sphalerite. — This mineral occurred in conjunction with galena at the Tui Mine in 
large quantities. It is very common in the Te Ai-oha ores, also associated with galena. 
It occurs in the unoxidized portion of the Maria lode. 

Antimony. — Analyses of the concentrates from the Karangahake and Te Aroha 
districts disclose the presence of antimony in small quantity. In the analyses of 
Talisman ores, quoted elsewhere, antimony occurs, and seems to decrease as the copper 
and silver content decreases. It is suggested that some form of tetrahedrite occurs, but 
as silver is also plentiful pyrargyrite may occur. Pond* long ago showed that pyrargjnrite 
probably occurred at Karangahake. 

Arsenic. — Occurs in concentrates from Te Aroha in small quantities,! perhaps in 
proustite. 

Facts observed in connection with the Ore-beposits. 

Propylitization. 
The first fact which strikes the investigator of ore-genesis is that the lodes within 
the subdivision, and similar .lodes in volcanic rocks elsewhere, are contained in a type 
of rock which has so many characteristics pecuhar to itself that for a long time it was 
regarded as a separate rock - species. To designate this rock - species, the name 
" propylite " or " greenstone trachyte " was used. It was found, however, that 
propyhtes even in the same locahty varied greatly, and it was demonstrated that 

* Pond, J. A. : Mines Reports, 1887, p. 56. 

t Pond, J. A. : Mines Reports, 1887, pp. 57 and 59. 

J Park, J. : " On the Occurrence of Rare Minerals in New Zealand," Trans., vol. xxvi, 1893, p. 366. 

§ Mines Reports, 1890, p. 44. 



93 

propylites graded int.) other volcanic rocks, sometimes into andesites, sometimes into 
dacites, sometimes into phonolites, and sometimes into volcanic breccias ; in fact, it 
was proved that propyhtes are but an altered phase of other volcanic rocks. Ordinary 
atmospheric weathering does not produce this alteration, and it has been shown that 
the only agents competent to do so are the heated emanations connected with the 
waning phase of vulcanism. From observations of existing fumaroles and solfataras it 
has been found that according to the temperature so does the composition of the issuing 
gases vary. Thus, while all contain steam as their principal constituent, only the 
hottest carry fluorine, chlorine, and boron ; as the temperature falls, sulphur in the 
form of sulphuretted hydrogen and sulphur-dioxide becomes prominent, and finally 
carbon-dioxide is given off in large quantities. 

Fumaroles which emit carbon-dioxide as their principal constituent (omitting 
• steam) are by far the most numerous, and from this it is argued that the carbon-dioxide 
stage is the most prolonged in the life of a fumarole. In the end the aqueous vapour 
condenses, and the fumarole becomes a hot spring. Fumaroles in all stages of their Ufe- 
history occur in the hot lakes district of New Zealand. 

It is believed that the propyhtization of volcanic rocks is due to the long-continued 
action of fumaroles rising through zones of country sheeted by faulting. Such a theory 
accounts for all the facts in connection with propyhtization ; it explains the more 
intense alteration in the neighbourhood of fissures ; it provides the water and carbon- 
dioxide required for the chloritization of the ferro-magnesian minerals, the potash 
required for the sericite, and the sulphur and iron required for the formation of pyrite. 

Persistence of Lodes in Defth. 

In the majority of cases, wherever sufficient work has been done on the lodes of the 
Hauraki Peninsula, it has been found that they either do not hve down at all or are 
much reduced in size in depth. To cite examples from within the subdivision : The 
Crown reef, which averaged, say, 2 ft. in width over a length of nearly 700 ft. in the 
Waitawheta level, contracts to a few stringers in the crosscut from the Welcome lode, 
500 ft. below. Again, Shepherd's reef, in the Tahsman Mine, which in No. 8 level 
was a rather irregular reef, becomes in No. 12 level, 500 ft. below, a breccia-filled fissure, 
with no apparent veinlets of quartz or calcite. The great mass of quartz 40 ft. or more 
in thickness forming the crest of the hill over the Karangahake Railway tunnel dwindles 
to a few inches in the railway - tunnel 800 ft. below. At Te Aroha the great Buck 
Reef at the end of the drive from Waiorongomai is only 12 ft. thick, »vhile on the 
hill above it averages at least 80 ft. of quartz and silicified country. 

This diminution in si?.^ of lodes in depth is widespread over the Hauraki Peninsula. 
Thus the " Tokatea big x^ef," which on the outcrop is 30 ft. to 150 ft. in width, "is 
represented in depth by a fissure carrying much mullock and clayey material and very 
Httle quartz."* Again, in the Kapanga area, Coromandel, " the veins contract in width 
in the lower levels, and become poor."! In connection with the Thames area, " Mine- 
workings have made it quite apparent that the vein fissures near the surface greatly 
exceed in number those occurring at greater depths. Many of the parallel veins, 
apparently quite independent at or near the surface, on being followed downward 
terminate on the hanging-wall of the larger and more persistent reefs. "J Again, at 
Waitekauri in connection with the Golden Cross Mine : " Mining developments below 
the 500 ft. level, moreover, have gone to show that these calcite bodies§ themselves lens 



* Fraser, C. ; Bulletin No. 4. p. 121. 

t|Op. cit., p. iOO. 

i Fraser, C. : BuUotiu No. 10, p. 34. 

S " These calcite bodies " cut out the quartz of the upper levels. 



94 

out rapidly in depth, and give place to rock exhibiting sheeted fracturing — numerous 
parallel joints, narrow fissures, and pug-filled shattered zones in which httle or no calcite 
or quartz has been deposited."* At Waihi, however, in the deepest levels opened the 
lode-filhng continues downward as strongly as ever. Thus in nearly every district in 
the Hauraki Peninsula where mining operations have been pushed to a considerable 
depth a tendency for the lodes to decrease in number and also in size has been noted. 

Oangue. 

It has already been noted that quartz, pseudomorphous after calcite, occurs in many 
of the lodes of the subdivision, and that in a lesser number of lodes calcite makes its 
appearance in depth. Thus the Crown reef, in the crosscut from the Welcome reef 
in No. 5b level, consists of calcite stringers. Again, in the deepest portion of the 
Talisman Mine, on driving along the fissure, rich quartzose ore gives place to calcite 
mixed with quartz in a much - contracted fissure. At Waiorongomai the Premier lode 
as developed in the lowest adit contains a considerable proportion of calcite, whereas 
above calcite was entirely absent. 

Without the subdivision, at Waitekauri* and Waihi| calcite occurs in increasing 
amount with depth, and many of the lode fissures are entirely filled with calcite in the 
lower levels. Again, at KuaotunuJ much of the quartz is pseudomorphous after calcite. 
Calcite is also a mineral in connection with the reefs of Tokatea Hill, but occurs with 
less frequency at Kapanga and Thames. 

It may be taken as established that in many of the lodes of the subdivision — 
and, indeed, of the whole of the Hauraki Peninsula — quartz, pseudomorphous after calcite, 
forms a considerable proportion of the gangue of the lodes ; that with depth an increasing 
amount of calcite and a decreasing amount of quartz is apparent in these lodes. 

Distrihutio')i of Metallic Contents oj Lodes. 

Other facts observed are those connected with the distribution of the metalhc 
contents of the lodes. Within the Aroha Subdivision all the lodes have an oxidized 
upper portion, which consists of quartz stained by oxides of iron and manganese. The 
gold occurs in small specks, which may often be seen without the aid of a lens ; the 
silver occurs mainly as argentite. In the oxidized zone copper and lead carbonates, 
lead-sulphate, copper-silicate, and (rarely) haloid salts of silver are present. Sulphide of 
iron IS the prmcipal sulphide salt, and this often occurs in the black sooty form 
known as " sulphuret." In the Karangahake area this oxidized portion may extend 
500 ft. below the river-level, and it is only in the southern portion of the Maria lode 
that unoxidized ore is found. In this portion of the Tahsmau Mine the payable ore 
comes in at No. 8 level, beneath an extensive zone of lean oxidized ores. The apex 
of the shoot consists of high-grade quartzose ores containing gold and silver in the 
proportion of about 1 to 4. A considerable amount of wad occurs in connection with 
the cellular quartz. The ore at this point, in fact, is a rich oxidized ore. Followed 
down, the character of the ore changes, more pyrite occurs, carbonates of copper, and 
occasionally covelhte, the latter always associated with very rich ore. Lower still 
bands of heavy sulphide ore are found, argentite becomes more plentiful, and occasionally 
wire silver is observed, chalcopyrite and galena and a httle sphalerite, and (rarely) 
rhodochrosite may be detected. Followed farther down the silver-content gradually 
decreases, copper also shows a decrease with depth, while lead and zinc increase. 
Rhodochrosite does not seem to vary much with depth after its first appearance. 



* Bell and Fraser : Bulletin No. 15, p. 111. 
t Op. cit., p. 138. 

I Park, J. : "Geology and Veins of the Hauraki Goldfields," Trans. N.Z. Inst. Min. Eng., vol. i, 1897, 
p. 100. 



95 



The length of this shoot along the strike of the fissure shows an increase, up to the 
present date, with each descending level. Again, as each level is driven through the 
rich ore, beyond the Umits of the shoot, a variation in the fissure-filling is noticeable 
— the amount of calcite in the barren ore increases with depth until, at No. 14 level, 
the barren filhng is almost entirely of calcite, mixed with a small quantity of other 
carbonates. 

The following analyses of ore from the Bonanza section of the Maria lode, taken 
at approximately 200 ft. intervals, may be quoted. The writer is indebted to 
Mr. H. Stansfield, of the Tahsman Consohdated, for specimens Nos. 1 and 4. Nos. 2 
and 3 are quoted from A. Jarman's paper on the Tahsman Mine.* 





No. 11 Level. 


(2.) 
No. 12 Level. 


(3.) 
No. 13 Level. 


(4-) 

Intermediate, 

80 ft. below No. 14. 


Gold 

Silver 

Copper 

Antimony 

Lea'd 

Zinc 

Iron 

Sulphur 

Aluminium . 

Manganese . 

Silica (insolu 


ble) '. 






0-197 
1-411 

Nil 

15 

3-64 
0-19 
0-22 

Nil 
91-92 


0-126 
2-392 
3-24 
0-42 
6-0 
2-4 
8-74 
7-4 
1-2 
1-07 
65-64 


0-117 
0-499 
2-0 
Trace 
2-21 
3-4 
8-54 
5-5 
1-35 
0-90 
74-54 


0-111 

0-075 
2-70 

9-50 
14-75 

6-13 

13-84 

n.d. 

2-88 




97-578 


98-628 


99-056 




Gold, per long ton . . 
Silver „ 


Oz. dwt. gr. 

64 5 12 

460 9 11 


Oz. dwt. gr. 

41 1 13 

781 4 11 


Oz. dwt. gr. 

38 2 18 

163 1 18 


Oz. dwt. gr. 
36 3 9 
24 7 1 



The manganese probably occurs in Nos. 2, 3, and 4, as carbonate. 
The constituents of these samples, the first excepted, with the omission of sulphur 
and siHca, have been recalculated centesimally as under :^ 

Gold 

Silver 

Copper 

Antimony 

Lead 

Zinc . . 

Iron . . 

Aluminium 

Manganese 

At Te Aroha the oxidation of the ore has not proceeded nearly so far as at 
Karangahake, and in most of the lodes sulphides occur close to the surface. Owing 
to the depressed state of the mining industry, and the consequent fewness of the 
levels open, but few data relative to mineral-content in unoxidized ore could be 



(2). 

0-49 


(3.) 

0-61 


(4.) 
0-31 


9-35 


2-62 


0-21 


12-66 


10-52 


7-48 


1-64 


Trace 




23-45 


11-62 


26-30 


9-38 


17-88 


40-84 


3416 


44-93 


16-93 


4-69 


7-09 


. . 


4-18 


4-73 


7-93 



* Jarman, A. : " Mining and Ore-treatment at the Talisman Mine, Karangahake, N.Z.," Trans. Aust. 
Inet. Min. Eng., vol. xvi, 1912, p. 343. 



96 

obtained. In the Premier the gold-silver ratio was, in the iijiper levels, 1 to 4 ; in the 
lowest level in which stoping has been done the ratio was 1 to 2-|. Again, in the 
case of the Tiii Mine, the writer was informed on good authority that the outcrop 
showed sulphides of lead, zinc, and a little mercury, as well as sulphate and carbonate 
of lead, while in depth the cinnabar was altogether absent, and the sphalerite increased 
relatively to the galena. Again, in the mines at Waiorongomai the copper-pyrites of 
the upper levels showed a tendency to give place to sphalerite in depth. It may also 
be mentioned that here, as at Karangahake, copper-pyrites is a good indicator for gold. 

Taking the precise information gathered at Karangahake, and combining it with 
the vague data from Te Aroha, it will be noted that in following downward the 
unoxidized ore of these locaUties the sulphide of each metal increases, attains a maximum, 
and then decreases. Furthermore, the order in which the maxima are attained corresponds 
well with the order of solubiUty of metalUc sulphides, as determined by Anthon long 
ago,* and by Schiirmann in 1888. Schiirmann's table, of which the first member is 
the most insoluble, " indicates the order of deposition of sulphides from a mixture of 
metalhc salts when such a mixture comes into contact with an excess of sulphide — 
e.g., iron-sulphide. . . . An observed succession in the field may therefore indicate 
either the direction of the flow of the solution which produced the deposition or the 
direction in which to seek the more precious metal, "f 

The following table contains the results obtained : — 



Schiirmann's 
Succession. 


Observed Succession. 


Remarks. 


Palladium 


■• 


The succession — silver, copper, lead, and zinc — has 
been actually observed. 


Mercury 


Mercury 


The position of mercury is fixed in the Aroha Sub- 
division only in respect to lead and ziac. 


Silver 


Silver . . 


, , 


Copper 


Copper 




Bismuth 






Cadmium 






Antimony 


(Antimony) 


Antimony occurs in largest quantity when copper and 
silver are present, and is probably combined as 
pyrargyrite or perhaps as tetrahedrite, but analyses 
are insufficient to fix more accurately its position in 
the succession. 


Tin 






. . >• 


Lead 




Lead 








Zinc 




Zinc 








Nickel 












Cobalt 












Ferrous iron . 












Arsenic 












Manganese 













Notwithstanding the imperfection of the observations, it may be taken as proved 
that the succession — mercury, silver, copper, lead, zinc — holds for the explored unoxidized 
ores of the Karangahake and Te Aroha mining-areas. In regard to the other mining- 
areas of Hauraki Peninsula the data available on this point are very meagre, but the 
analyses of sulphide ore from the Colorado ClaimJ indicate a similar succession. 



* Jrn. prakt. Chem. vol. x, 1837, p. 353. 

t Wells, R. G. : "Fractional Precipitation of Sulphides," Economic Geology, vol. v, 1910, p. 6. 

% Bulletin No. 10, p. 59. 



97 

Influence of Faults, &c. 

The influence of intersecting veins, faults, cross-courses, flinties, and pyritic veinlets 
on the localization of ores in the lodes of the Hauraki Peninsula is so well known that 
it is unnecessary to dwell on this point further than to mention examples from the 
Aroha Subdivision. At Karangahake, as a study of the stope sections of the lodes 
will show, fault intersections have a considerable influence on the disposition of payable 
ore. In the great majority of cases the more valuable ore is found on the hanging- 
wall side of the fault. Intersecting veinlets have also played an important part at many 
places. At Te Aroha, as before mentioned, a number of north-east striking lodes reach 
a north-and -south lode at acute angles, and at a considerable number of the junctions 
rich ore has been found. Again, in the Bonanza section of the Maria lode it was 
pointed out to the writer that higher values were often to be found in the main lode 
where small oblique stringers run into it. 

Influence of Present Topoyraphy. 

Another set of data bearing on ore-genesis is aft'orded by the distribution of the 
ore in respect to topography. The lodes of the Karangahake area traverse longi- 
tudinally an oblong block of country. This block of country is crossed at its northern 
end by the Ohinemuri and Waitawheta rivers. Between these rivers lies Taukani Hill 
(815 ft.), and the lodes traversing this hill carried valuable ore on their outcrops and 
some distance below (400 ft.). South of the Waitawheta the great face of the end of 
the mountain -block rises to a height of over 1,800 ft., freed on its east and west flanks 
from the neighbouring rocks by faulting and erosion. It is only the three persistent 
lodes outcropping on the terminal face of the mountain block which have been found 
to carry large quantities of payable ore. These are the Crown, Welcome, and Maria 
lodes. When these lodes are followed southward along their strike into the hill the 
lode fissures decrease in size, and the ore changes in value. Thus the Crown and 
Welcome lodes were followed in the Crown Mines until no longer payable, and the 
Welcome lode has been explored still farther south in the Tahsman Claim by a crosscut 
east from No. 11 level, the lowest water-free level. At the time of the writer's visit 
the air in this crosscut was too poor to permit the examination of the lode from this 
point, but the management stated that 555 ft. had been driven along the lode, which had 
well-defined walls. For 400 ft. in the northern portion of the level the lode varied from 
3 ft. to 5 ft. in width, and consisted of an equal mixture of white quartz and calcite, with 
frequent inclusions of country. Sulphides occurred only north of the intersection of 
the crosscut, where a few " pencil veins " of dark ore, assaying from £1 10s. to £3 per 
ton in bulUon, were met with. These were further explored by rise and winze, but 
showed no improvement. For the last 50 ft. in the south end of the drive the fissure 
was filled with crushed country without gangue-material. In the case of the Maria 
lode, in No. 11 level, just about opposite this point a similar change occurred. 

In depth, development has shown that all the lodes of the area except the Maria 
lode decrease in size and carry ore of a lower tenor. 

At Te Aroha the distribution of the ore in the fissured belt is very remarkable. 
To recapitulate briefly the structvire of the field : A north-east striking series of ore-bearing 
lodes cross obliquely a north-striking siUcified zone. The lodes striking north-east are 
exceedingly numerous, and seem to belong to an extensive sheeted zone of country. 
The Waiorongomai flows southward parallel to and from 40 to 50 chains from the 
silicified zone, or Buck Reef. Army Creek, Diamond Gully, Canadian Gully, and Premier 
Creek cross the lode-bearing area of country, and produce series of exceedingly steep 
slopes and spurs, and it is where the north-east lodes cross these slopes that they carry 
ore. Thus the Silver King lode is the only one to cross the slope south of Army 

7 — Aroha. 



98 

Creek, and it carried ore in what are known as the Big Blow workings, some 5 chains 
from its junction with the Buck Reef. The north slope of Army Creek becomes the 
main slope to the Waiorongomai, and on this occurs ore in the Werahiko, Waitoki, 
Silver King, and Seddon lodes. On the south slope of Diamond Grully the EngUsh 
Army, Goldsworthy, Welcome., Moa. East-and-West, Loyalty, Palace, and Phoenix lodes 
carry ore. On the north slope of Diamond Gully are the Eureka, New Find, Arizona, 
Diamond Gully, Wellington, Galena, May Queen, Inverness, and- F. lodes. On the 
spur between Canadian Gully and Premier Creek are the Vulcari, Colonist, Hero, and 
A¥arrior lodes ; while north of the Premier Creek the Vulcan (here known as the Premier) 
carries ore where it enters the Buck Reef. 

It may be urged that steep slopes afford excellent op])ortunities for i)rospecting 
and that consequently the ore of the slopes has been found, while that occurring on 
the flat tops of hills or near creek-beds has not. Such a contention mil not hold ; ah 
the surface has been searched many times. Moreover, the rich shoots could not bft 
traced beyond the steep slopes, while in the creek-beds the large reefs are nearly all 
represented by silicified country, or at most by a few stringers. 

The Champion lode, to the west of Te Aroha Mountain, outcrops along the steep 
western slope of the mountain, so that its ore-shoots — the Montezuma, Ishngton, Tui, 
and Mikado — are necessarily connected with steep slopes. 

In the Waitakohe area, near Katikati, the lodes outcrop on a steep spur, and at 
Owharoa the valuable ore does not seem to go below the drainage-level. 

In regard to the other mining-areas of the Hauraki Peninsula, Eraser and Adams 
say of the Coromandel Subdivision : " All the important ore-shoots discovered in this 
area have been mined from within 800 ft. and mostly 4-00 ft. of the present land-surface, 
irrespective of its topography "* ; and, again, of the Thames Subdivision, " The down- 
ward Umit of the pay-ores mined appears to conform roughly to surface-contours. "f 
In connection with the Waihi-Tairua Subdivision the same thing is said, the Waihi 
area being excepted.} 

It may be ta.ken as established that in the majority of the mining districts of 
Hauraki the existing topography exercises a very marked influence on the distribution 
of the ores. 

Nature of Country. 

It has already been stated that the country enclosing the Maria lode consists of 
beds of different classes of volcanic rocks. These different rocks do not seem to affect 
in any way the value of the ore contained in the lode. Thus rich sulphide ore occurs 
when andesite, breccia, and fine-grained tuff form the enclosing country. The oxidized 
ore of the Karangahake mining-area is enclosed in rock so altered by propyhtization 
and subsequent weathering that its exact nature is usually indeterminable, but it is 
at least in part an altered spheruhtic dacite. Rich ore has also been found in a similar 
dacite at Owharoa. At Te Aroha the country of the lodes seems to be chiefly andesite, 
although an andesite breccia is reported to have occurred in parts of the New Find 
working. At Waitakohe the rock is andesite. 

■ In the Aroha Subdivision, as in other mining-areas of the Hauraki Peninsula, a 
distinction between " kindly " and " dead " country is made by miners. There are 
also various kinds of each class of country. In different mining-areas apparently 
similar rocks would be put in different classes. Thus the unhkely country of Waihi 
is very similar to some of the kindly country of Karangahake. The " mottled " 
country or breccia of Karangahake would be considered as unhkely to carry rich ore in 
the Thames area. Again, the country of the Te Aroha lodes is much harder than that 



* Fi-aser and Adams, Bulletin No. 4, p. 106. f Eraser, C. : Bulletin No. 10, p. 45. % Bell and Eraser ; 
Bulletin No. 15, p. 65, 



09 



of tlie Thames lodes. It will thus be seen that tliere is no constancy in appearance of 
the Ukely and unhkely country in the different mining-areas. Nevertheless, in each 
mining-area " kindly " and " dead " country may be. distinguished. " Kindly " country 
for each locaUty is country in which the lodes of that locahty may carry valuable 
ore, while " dead " country is country in which the lodes become barren and small, 
or pinch out altogether. In fact, the distribution of " kindly " country is dependent 
upon the distribution of the lodes, which in turn is dependent upon the present 
topography. 

Naitire of Mwe-waters. 
At Te Aroha all workings are level-free, and the waters met with must be regarded as 
surface-waters. At Karangahake the Talisman and Crown mines pump considerable 
amounts of water. In the Tahsman the surface-water is caught at No. 7 level, and is not 
allowed to reach the deeper workings. This mine, from its two shafts, is pumping in all 
45,000 gallons per hour. The water from part of the Crown Mines — the winzes below No. 5b 
level in the southern portion of the Welcome lode — is also hfted by the Tahsman pumps, 
but the main supply of water pumped by the Crown Mines is apparently independent 
of the Tahsman water-system. Seepage from the Waitawlieta to the Talisman workings 
is impossible, seeing that none of the workings of the mine below No. 11 are near 
that stream ; and, moreover, the main supply of water (35,000 gallons per hour) is dealt 
with by the pumps in the Tahsman shaft, and not by those of the Woodstock shaft, 
which is only 260 ft. from the Waitawheta. The water pumped from the Tahsman 
Mine must be derived from the sea of underground water. A sample — of which an 
analysis is 'given below — was taken from a strong stream issuing from the cavernous ore 
in the face of the intermediate level, 81 ft. below No. 14 level and 90 ft. north of 
No. 12 winze. The temperature of the issuing water was 78° Fahr. For the sake 



of comparison, analyses of other mine-waters from Thames and Waihi have also 
tabulated. 



Sodium-chloride . . 

Sodium-sulphate 

Sodium-bicarbonate 

Potassium-ch loride 

Calcium-chloride 

Calcium-sulphate 

Calcium-bicarbonate 

Baryta . . 

Magnesium-sulphate 

Magnesium-bicarbonate 

Ferrous bicarbonate 

Aluminium-sulphate 

Alumina 

Sodium-silicate . . 



Free carbon-dioxide 

Temperature, Fahr. . . 92° . . . . . . 78° 

(1.) From 1.000 ft. level. Tliames-Hauraki shaft. Bulletin No. 10, p. 49. 
(2.) From 1,150 ft. level. No. 5 shaft. Waihi Mine, Bulletin No. 15. p. 69. 
(3.) From fissure 300 ft. from No. 5 shaft, Waihi Mine, Bulletin No. 15. [). m. 
(4.) From bottom of Waiiii Extended shaft. 1.040 ft.. Bulletin No. 15. p. 69. 
(5.) From the intermediate below No. 14 level, Bonanza Bection, Talianian. 
—Aroha. 



been 



(!•) 


(2.) 


(3.) 
per 100,000 
1-00 


(4.) 


(5.) 


. . 143-9 


0-60 


, , 




. . 1041 


5-50 


6-50 


8-40 


2-8 
4-4 




3-10 


3-40 


3-80 


2-5 


• . 


2-70 


3-85 




. . 


. . 157-0 


14-70 


19-20 


11-67 


8-1 


Trace 








. . 


24-9 


1-50 


2-10 


1-20 


2-1 


58-4 










0-4 


0-35 


0-50 


0-25 




120 


1 00 


1-70 


0-50 


0-3 


7-7 


2-40 


3-60 


315 


3-0 


508-4 


31 -85 


n-S5 


28-97 


23-2 
1-3 



100 



These analyses, recalculated centesimally after the ionic method, yield the following 



results :- 



Na 

K 

Ca 

Ba 

Mg 

Al 

Fe 

CI 

SO^ 

HCO. 

SiO, 



(1-) 

17-20 


(2.) 
7-24 


(3.) 
7-12 


(4.) 
9-27 


(5.) 
9-64 


Nil 


5-23 


4-18 


6-05 


n.d. 


7-70 


13-98 


14-12 


9-93 


12-26 


Trace 


n.d. 


n.d. 


n.d. 


n.d. 


2-89 


0-94 


1-08 


1-46 


1-64 


0-37 


0-69 


0-89 


0-38 


0-70 


0-03 


0-38 


0-38 


0-18 


. . 


17-33 


5-67 


5-28 


6-25 


7-01 


19-94 


23-79 


24-17 


5-00 


15-76 


33-26 


35-79 


35-59 


52-45 


39-85 


1-28 


6-29 


7-19 
41-85 


9-03 

28-97 


13-14 


(508-40 


31-85 


23-20 


( -• 






, . 


1-30 


92° 






.. 


78° 



Total sahnity ] Parts per 
Free COg ) 100,000 
Temperature . . 

From these results it will be noted that all the mine- waters, which in every case 
were collected from the deepest workings of the various localities, are sulphated and 
carbonated waters. They are probably descending waters of meteoric origin. The 
water now infiltering into old drives, &c., also contains sulphates, and some of these 
sulphates are deposited on the walls of the old workings as epsomite and melanterite. 

The following table, taken from Don,* shows the acidity and iron-content of 
mine-waters from Karangahake. The waters are from the vadose circulation : — 







Free Acid, in 


Free Acid, in ' S 5 S 


■s ° 


4^ OJ 




Country Rock. 


Reaction to 
Test Paper. 


Grammes per 

Litre, before 

Exposure to Air. 


Grammes per 

Litre, after 

Exposure to Air. 


Total Weig 
of Iron, 
Grammes j 
Litre. 


Iron prese 
as Ferr 
Salts. 


n prese 
Ferro 
Its. 


i 


HCl. 


H2SO4. 


HCl. 


H2SO4. 


M rt 

M 


b 


Propylite, highly py- 


Strongly 


0-287 


Nil 


0-592 1-384 


2-471 


0-946 


1-525 




ritous 


acid 






1 1 






c 


Propylite, highly py- 
ritous 


Acid . . 


0-065 


" 


0-208 Nil 1 1-086 


0-731 


0-355 


9 


Propylite, pyritous 


Acid . . 


0-409 


1-063 


0-605 ; 1-582 ! 1-903 


1-127 


0-776 



b. From Maria reef, Karangahake. Deposited a large quantity of ferric hydroxide 

on standing. 

c. From Woodstock reef, Karangahake. Deposited a large quantity of ferric 

hydroxide on standing. 
g. From Crown Mine, Karangahake. Nearly clear ; shght deposit of ferric hydroxide 
on standing. 

Physico-chemical Data. 
Another class of data, bearing on the genesis of ore, has been advanced by the 
physical chemist rather than by the geologist. These data deal with the effects of 
pressure and temperature on the crystalUzation of minerals. 

It has been shown that pressure has an insignificant effect upon crystalJization 
when compared with other factors ; thus a few degrees of temperature can counteract 
the effect of many atmospheres.f 

* Don, J. R. : " The Genesis of Certain Auriferous Lodes," Trans. Amer. Inst, of Min. Eng., vol. xxvii 
1898, p. 654. 

i Van't Ho£E, J. H. : " Physical Chemistry in the Service of the Sciences," Chicago, 1903, p. 123. 



101 

The effects of temperature are much greater. It is well known that calcium - 
carbonate crystalUzes out of a solution with a temperature exceeding 90° C. as aragonite. 
and out of a colder solution as calcite.* Thus, boiling springs deposit calcium- 
carbonate as aragonite, and cold springs as calcite. Again, it is well known that when 
aragonite is heated it is transformed to calcite, and this transformation may begin 
at 57° C.f 

In the case of siUcon-dioxide, Miiggef has shown that 570° C. is the inversion 
temperature between a and /3 quartz. 

Sulphide of iron crystalhzes in several forms. Pyrrhotite forms when the 
temperature is over 575° C, and marcasite when the temperature is under 400° C.§ 
Pyrite, the commonest form of all, has a much wider range. 

It is well known that covellite decomposes when heated, and at a temperature 
of 500° C. the dissociation-pressure is several atmospheres. || 

In general, it may be said that minerals formed under high pressures (at great 
depth) are characterized by a small molecular volume, while those formed at the 
surface tend to contain water. 

These physico-chemical data are of doubtful value, as it is impossible to reproduce 
in the laboratory all the conditions obtaining in nature. Thus it is impossible to 
reproduce exactly the chemical composition of the depositing solutions, and it is well 
known that the presence of only a small quantity of some substances greatly modifies 
the nature of the crystallization-product of a solution. 

However, the generalizations that pressure tends to cause the crystalUzation of 
minerals of small molecular volume, and has httle influence, other factors being favour- 
able, upon the crystalhzation of any particular mineral, may be accepted without 
reserve. 

Summary. 

The facts observed in connection with the lodes form the data upon which any 
discussion of the genesis of the ore must be based. These facts, as far as the Aroha 
Subdivision is concerned, may be summarized thus : — 

. (1.) Ore-bodies occur only in propyhtized country. 

(2.) The lodes decrease in number and size as depth is attained. 

(3.) Quartz pseudomorphous after calcite occurs in many lodes, and as depth is 

attained calcite itself appears and tends to displace the quartz of the gangue. 

(4.) In all lodes where unoxidizcd ore occurs the distribution of the sulphides in 

the unoxidized portion of the lodes shows that the depositing solutions were 

descending. 
(5.) Faults, cross-fissures, &c., have a marked influence upon the localization of the 

ore, and the ore-distribution suggests deposition from descending solutions. 
(6.) The present topography exercises a marked influence on the distribution of the 

ore in the lodes. 
(7.) The nature of the country influences ore-deposition, and the distribution of 

favourable country is dependent upon the present topography. 
(8.) The mine-waters carry large quantities of sulphates and carbonates. They are 

believed to be of meteoric origin. 

* Roscoe and Schorlemmer : " Treatise on Chemistry," London, 1897, vol. ii, p. 442. 

t Foote, H. W. : Zeit. Phys. Chem. vol. xxxiii. 1900, p. 740. 

X Mugge : " Ueber die Zustands iindening des Quarzes bei 570°," Neues Jahrbuch fur Min., &c., 1907. 
pp. 181-96. 

§ Allen, E. T. : " Studies in Ore-deposition, with Special Reference'to the Sulphides of Iron," Journal 
of the Washington Academy of Science, i, pp. 170-7 (1911). 

II Foote, F. W. : Economic Geology, vol. v, 1910, p. 485. 



102 

Genesis of the Ore. 

IntroduclioH. 

The data having a bearing upon the genesis of the ore have now been set forth. 
There remains the formulation of a theory which will satisfactorily explain all the 
facts of observation. In the very nature of the case, any theory of ore-formation is 
incapable of direct proof. Nevertheless, if a theory can be formulated which will satisfy 
each and every observed fact it may be accepted as a working hypothesis. Such a 
theory gains stability with each fact explained,, and, when the facts satisfied by the 
theory become numerous, deductions based upon the hypothesis may legitimately be 
made. 

Ascension Theory. 

The generally accepted theory of ore - genesis is that which postulates that ore- 
deposits have been formed by heated ascending waters. This theory was developed by 
European geologists, and its appHcabihty to many locaUties has been well estabhshed. 
Moreover, as already mentioned, it is possible to account for the propylitization of the 
country of the lodes only on the supposition that this alteration was brought about by 
the action of hot ascending aqueous solutions. Whether these solutions were " juvenile " 
or reascending meteoric waters is, for the purposes of this discussion, irrelevant. 

It seems but a natural step, if the propyhtization by hot ascending solutions l^e 
admitted, to account for the lode-filhng by the same means. That the hot solutions 
are competent to form lode-filUng is well known, and may be accepted as proved.* 
Cohn Fraser, in deaUng with the lodes of the Coromandelf and Thames subdivisions, J 
and Bell and Fraser, in connection with those of the Waihi-Tairua§ Subdivision, accept 
this theory. Nevertheless, although the lodes of the Karangahake and Te Aroha 
mining-areas are closely comparable with those of Waihi, Maratoto, Waitekauri, and to 
a less degree with the lodes of other mining-areas of the Hauraki Peninsula, the writer 
is constrained to reject this theory in connection with the economic deposits of the 
Aroha Subdivision. The facts that the lodes decrease in size and number in depth, 
that quartz pseudomorphous after calcite occurs in the upper levels and calcite in 
increasing amount in the lower levels, that the rich ore is generally found in the 
hanging-wall side of faults, and that the distribution of the ore is closely conformable 
to present-day topography — all are strongly suggestive of ore-deposition by descending 
solutions. The zoning of the sulphides in the lower unoxidized portions of the lodes 
is, in the writer's opinion, conclusive proof of the formation of these portions of the 
lodes by descending solutions. To elaborate this discussion the explanations offered 
by the respective hypotheses for each observed fact will be stated and critically 
examined. 

The fact that the lodes decrease in size and number as depth is attained is explained 
on the ascension theory by the precipitating influence decrease in pressure and 
temperature has upon the substances dissolved in the ascending solutions. That all 
lodes decrease in size with depth may be accepted as axiomatic, and that substances 
separate out from solutions with decreasing temperature is not denied ; but in districts 
where the ascension theory has been well established — Przibram, Freiberg, Clausthal, &c. — 
the diminution in size of the lodes is very gradual ; whereas in the case of the Hauraki 



♦ Weed, W. H. : " Mineral Vein-formation at Boulder Hot Springs, Montana," U.S. Geol. Siirvey, 2l8t 
Annual Rep., 1900, vol. ii, pp. 233-55. 

t Fraser, C, and Adams, J. H. : Bulletin No. 4, p. 100. 

% Fraser, Cohn : Bulletin No. 4, p. 34. 

§ Bell, J. M., and Fraser, C. : Bulletin No. 15, pp. 63, 132. 



108 

lodes the decrease is comparatively abrupt, and is difficult to explain unless it be 
supposed that deposition took place relatively close to the surface, probably being 
aided by conuuiiigUug with surface-waters. This accords well with the marked influence 
the present topography seems to have upon the distribution of the ore. There are, 
however, serious difficulties involved in the acceptance for all locahties of this view — 
i.e., that ascending solutions deposited their lode-material relatively near the surface, 
and on coming in contact with surface-waters. At Tokatea, Thames, Waihi (ignoring 
the younger rhyohtes), Karangahake, and Te Aroha the lode country is very much 
shattered, and has abrupt contours. In such shattered country as obtained at the 
time of the formation of the lodes it is evidently impossible that deposition from 
ascending solutions could have taken place on steep hillsides and on the tops of hills ; 
by the simple operation of the law of gravity the solutions would escape by the lowest 
opening, just as at the present day the hot springs issuing along fault-fractures- escape 
at the lowest available point. If the ore was deposited from ascending solutions there 
is no escape from the conclusion that quite extensive denudation has taken place since 
the formation of the lodes ; and, this admitted, explanations must be found for the 
facts that alluvial gold has hitherto not been found save in trivial quantities, and 
that the ore-distribution closely conforms to the present-day topography. For the 
first fact, the explanation that the alluvial gold is deeply buried beneath recent sands, &c., 
is feasible enough, but becomes unconvincing when appUed to half a dozen different dis- 
tricts, while to account by denudation alone for even a rough conformity of the ore-bodies 
witli present surface-features for every mining-area is impossible. 

On the ascension tlieory, the facts of observation in connection with the distribution 
of quartz and calcite within the lodes are explained on the assumption that after the 
fissures had been filled with calcite a reshattering permitted the uprising of solutions 
of a character different from those which formed the calcite-filhng.* This explanation 
is inapphcable where no shattering of the original calcite-filling has taken place, as in 
the Crown and Maria lodes. 

The zoning of the sulphides in vertical extent obtaining in the unoxidized portions 
of the lodes is inexphcable by the ascension theory, and the same may be said in 
connection with the distribution of favourable country. 

Secondary Enrichment Theory. 

There are thus several strong objections to be urged against the theory of ore- 
deposition by ascending solutions as appUed to the lodes of the Hauraki Peninsula. 
There remains the hypothesis which postulates deposition from descending waters. These 
waters could only have a meteoric origin, and there are two possible sources for the 
materials of the ore-bodies — either these are derived from previously existing lodes or 
from the country enclosing the lodes. 

The most obvious source for the ore-material is from previously existing lodes 
which had been formed during or after propyhtization by ascending waters. These lodes, 
which may be termed primary lodes, need not have contained the ore-materials in a 
concentrated form ; all that this theory requires is that the primary lodes contain all 
the materials contained in the secondary deposits. By the theory of " secondary 
enrichment " by descending waters a great inimber of facts observed in connection 
with the lodes may be readily explained. An extensive hterature has grown up round 
this phase of ore-formation, and the processes of solution, transportation, and redeposition 



* Bell. J. M.. and Fraser, 0. : Bullotin N... 15, 1912, p. 134. 



104 

have been ably discussed, and are now well understood. The papers of the modern 
American school of economic geologists may be consulted for a full discussion of this 
theory, which offers an adequate explanation for the zonal distribution of sulphides in 
ore-bodies, and for the influence the present topography has upon the distribution of 
" kindly " country and ore-bodies. 

The difficulty in the acceptance of this view when applied to the ore-deposits of 
the subdivision arises when inquiry is made concerning the nature of the primary ore- 
deposits from which the ore-bodies at present existing have been derived. The abund- 
ance of quartz pseudomorphous after calcite, and of calcite itself, in the lower portions 
of many lodes indicates that calcite formed the principal portion of the gangue of 
the primary ore-deposit. This is the conclusion reached by Bell and Fraser in con- 
nection with the lodes of Waihi, Waitekauri, Maratoto, and Komata.* It is evident 
that the small quantity of quartz contained in the calcite is insufficient to supply the 
quartz now forming the gangue of the " secondary " ore-deposits, and some other 
source of quartz must be found. Bell and Fraser derive it from later ascending solu- 
tions, but, from reasons already given, such a source is improbable. There remain the 
wall-rocks as a possible source for the quartz. Again, when the " primary " deposits 
of calcite are examined, it is found that although the wall-rock in the immediate 
vicinity be impregnated with pyrite the calcite itself is entirely free from sulphides, 
and it becomes necessary to derive the sulphides from the wall-rocks also. If both 
the gangue and the sulphides of the " secondary " ore-deposits are to be derived from 
the country, there is no necessity to postulate the existence of a primary lode. The 
facts that the calcite lode-filling of the Golden Cross Mine of Waitekauri cut out entirely 
in depth, that the calcite fissure-filling of the Karangahake area is much contracted 
when compared with the quartz - filling, and that lode-filUng of all description tends 
to disappear when the Welcome and Maria lodes are followed south, although the 
country, which is still strongly propyhtized, shows that not all of even the strong 
dominant fissures were filled during or after propylitization. Although on this point 
the observed cases are insufficient for safe generahzation, it may be stated that the 
calcite lode-filling as well as the ore-deposits tends to conform with the present topography. 

Lateral Secretion Theory. 

It is thus found that in some cases at least both gangue and ore have probably 
been derived from the country, and in no case is there proof that primary lode-filhng 
deposited by ascending solutions ever existed. Let us, then, examine the competence 
of the country as a source from which the materials forming the ore-bodies may be 
derived. The writer believes, and has advanced arguments for this behef, that propy 
Utization preceded lode-formation in every case. By country, then, propyhtized rock is 
impHed. That propyhtized rock can supply quartz, calcite, and other carbonates 
there is no doubt. Microscopic examination shows that propyhtized rock consists 
of quartz, sericite, and calcite, abundant in the above order, with a variable admixture 
of pyrite. Chemical analysis shows that in all rocks, even the most altered, which 
contain no trace of chlorite, there is a proportion of manganese and magnesium present, 
probably as carbonate. Now, as already pointed out in connection with the weathering 
of propyhtized rock, the descending solutions carrying carbon-dioxide readily leach out 
calcite from the upper levels and redeposit it lower down. The sericite is destroyed 
more slowly by the action of sulphuric and carbonic acids, and the siUcic acid derived 
from this decomposition deposits silica at a lower level. The siUca may take the 

* Bell, J. M., and Fraser, C. ; Bidletin No. 15, p. 53. 



105 



form of crystalline quartz, or chalcedony. Solution and deposition are continually 
in progress, and the more soluble calcite gains ground on the sihca. Thus two zones 
of deposition occur, characterized, the lower by calcite, the upper by sihca. Where 
elevation and denudation are the rule the zone of sihca-deposition constantly encroaches 
on the zone of calcite-deposition, which in turn moves downward into the unaffected 
propylite. Carbonates other than that of calcium are likely to be deposited with the 
calcite ; thus carbonates of magnesium, iron, and manganese occur, contaminating the 
calcite, as the following analyses show : — 



Insoluble in HCl, SiO^ 

Fe.O.,, Al.Oj 

FeO 

MnO 

CaOj 

MgO 

CO, 
Moisture and organic matter 



(1.) 

. . 0-65 


(2.) 
17-40 


(3.) 
28-46 


. . 040 


0-15 


0-27 


. . 3-20 


1-78 




.. 53-35 


44-50 


39-20 


.. 015 


015 


1-10 


.. 42-25 


35-58 


30-35 




[0-44 


0-62 



10000 



100-00 



100-00 



(1.) Empire lode, No. 5 level, Waihi Grand Junction Mine. Bulletin No. 15, p. 133. 
(2.) Martha lode, No. 5 level, Waihi Grand Junction Mine. Bulletin No. 15, p. 133. 
(3.) Maria lode, intermediate level, 81 ft. below No. 14 level, Tahsman Mine. 

Manganese-carbonate is not so readily soluble as calcite,* and tends to lag behind 
and enter the quartz-deposition zone. The other lode-minerals — valencianite and alunite 
— are also readily derivable from the sericite of the country rock. 

Deposition of the carbonates and sihca takes place in whatever open spaces exist 
underground. Fault fractures and joints form the greater part of these open spaces, 
and in them the calcite and quartz accumulate. Fault fissures were probably 
originally filled with crushed rock, and this crushed rock is replaced metasomatically 
by calcite and quartz. The removal of great quantities of calcite and silica from 
weathered rock causes incipient lines of weakness in the rock, induced by the stress 
which produced the main fractures to open, and these are filled with infiltering siUca. 
The porous rock itself may be silicified extensively. These stringers of quartz naturally 
decrease in number, and eventually die out as depth is attained. 

It will thus be seen that the country is competent to supply all the gangue-materials 
of the lodes, and that the distribution of the various gangue-materials is reasonably 
explained by the action of descending meteoric solutions. 

Let us now examine the country as a possible source for the metals of the ore. 
Don,t in his classic investigation on the origin of gold, found that the country of all 
the districts he examined was barren, as far as gold and silver were concerned, unless 
pyrite was present. He examined nine samples of rock from the Karangahake area, 
and tabulated his resultsj as follows : — 



♦ Roscoe and Schorlemmer : " Treatise on Chemistry," 1897. It is stated in vol. ii, p. 443, that 1 litre of 
water saturated with carbon-dioxide dissolves 0-88 gramme of calcium-carbonate at 10° C. ; and in vol. ii, 
p. 929, that 1 litre saturated with carbon-dioxide dissolves about 0-25 gramme of manganous carbonate. 

f Don, J. R. : " The Genesis of Certain Auriferous Lodes," Trans. Amer. Inst. Miu Eug., vol. xxvii, 
1898, pp. 564-668. 

J Loc. cit., p. 659. 



106 



Analyses of Samples frwn the Vadose Region, Karangahahe. 





IB 






^ 


» _ 




O 


II 


» 




M © 


ft 

g 




S o 

II 


CO 


ft. 


<1 



Lood.lity. 



Weight of 

Concentrates 

(panned). 



^ 



^ 






'^ 



o o 



'o 



cap^ 



■^^ 



Ft. 
10 



Ft. 
30 



20 180 
20 350 



10 

60 

25 
10 



From a cliff ou the 
tramway between 
the Crown Mine 
and Karangahake 

From a fault 



30 120 East of Maria reef 



I 
80 ' 3 



60 

24 

600 
660 



G r e^a^t Woodstock 

tunnel 
From cliti: in Waita- 

wheta near Crown 

Mines 
Foot - wall side of 

Crown reef 

Hanging-wall side of 
Crown reef 

From a fault exposed 
on tramway be- 
tween the Crown 
Mine and Ka- 
rangahake 



Lb. 

448 



rji'ains. 
1,634 . . 



1-12 I All assayed 
4-48 1,065, with a good 
I percentage of 
pyrite 
4-48 ' 873^ with good 
proportion of 
j pyrite 
1-12 ! All assayed 

2-24 



4-48 846, with a large 
percentage of 
sulphides 

2-24 617, nearly all py- 
rite 

1-12 All assayed 



Grains. 
00014 



00090 
00062 



Nil 

0-0095 
00013 

Nil 

0-0093 
00071 



Grains. 
0-7 



18-0 
. 31 



Nil 

190 
1-3 

Nil 

9-3 
14-2 



Grains. 
0-0018 



0-0036 
0-0054 



Nil 

0-0034 
00042 

Nil 

0-0126 
0-0014 



Grains. 
0-9 



7-2 
2-7 



Nil 

6-8 
4-2 

Nil 

12-6 
2-8 



a. Nearly white propyhte ; showed a good percentage of pyrite. 

b. Ferric oxide and higher oxides of manganese, with a httle quartz. 

c. Solid hard andesite, oxidized to brown colour on outside. Showed a good 

deal of pyrite. 

d. Hard greenish hypersthene andesite. Showed a good deal of pyrite. 

e. Ferric oxide and higher oxides of manganese, from a vein near the foot- 

wall of the Great Woodstock reef. 

/. Andesite ; brown, much decomposed. No pyrite visible. 

h. Greyish-white andesite, much oxidized on the outside, but showing pyrite 

freely when broken. 
i. Nearly white very sihceous rhyohte. Showing pyrite freely. 
j. Ferric oxide and higher oxides of m.anganese. 

The propylitized rocks of the vadose region of Karangahake, on an average of 
nine samples, thus yielded 7-29 gr. of gold and 4-13 gr. of silver per ton. 



107 

The other metals occurring in the lodes — copper, lead, and zinc — have not been 
sought in the country rock of the lodes within the subdivision, but it may be safely 
assumed that the pyrite of propylite carries these as well as gold and silver. 

The means of transport for the metals from the country to the lode must now 
be considered. This work, of course, is performed by the circulating solutions. The 
nature of these solutions has already been shown on a previous page.* 

It has been proved experimentally that gold may be dissolved by waters similar to 
those of Karangahake. The sulphates of silver, copper, zinc, and iron are all readily 
soluble in water, while lead-carbonate dissolves easily in water containing carbon-dioxide. 
The writer beheves, however, that these metals have been transported as sulphides by 
the solutions of alkaline carbonates, as well as in the form of sulphates and bicarbonates. 

The next question for consideration is why the minerals should be precipitated 
in the lode fissures. The sulphides are usually more generously disseminated in the 
country rock next the lode fissures, and the tendency is for the circulating solutions 
to use the more open channels. Thus the solutions from a wide extent of country 
drain into the fissures through the sulphide-rich walls. Precipitation is, at least in part, 
brought about by the mingling of solutions of shghtly different composition. This is 
indicated by the influence shown on ore-deposition by faults and cross-lodes. Again, 
there is a great deal of metasomatic replacement of the country of a fissure, and the 
jjyrite contained in large quantities in the fissure-wall may well have acted as the 
precipitant for the metals of the ore. In this connection the position of iron in 
Schiirmann's table indicates that iron-sulphide is capable of precipitating nearly all 
the metals, known to occur in the lodes, as sulphides. 

There is another point worthy of notice, and this is the great difference in the 
proportionate amount of iron in the sulphides occurring in the country and in the 
sulphides found in the lode. In the country the sulphides are iron-sulphides, with 
at most but a trace of other metals ; while in the lodes the analyses quoted oi\ page 95 
of this report indicate the composition of some samples of sulphides. The reason tor 
this seems to be the ease with which iron forms insoluble hydrates. These hydrates 
stain immense masses of oxidized propyhte. The writer, however, does not regard 
this explanation as entirely sufficient. 

Conclusion. 

The theories which derive ore-bodies by deposition from ascending solutions, by the 
secondary enrichment of previously existing lodes, and by deposition from descending 
solutions which derive their materials from the leaching of the enclosing rock, have been 
reviewed in connection with the ore-deposits of the subdivision, and the objections to 
each theory discussed. The writer puts forward the following hypothetical course of 
events as leading to the formation of the ore-deposits : — 

(1.) Orogenic movements produced faulted and sheeted zones of rock. These formed 
channe.ls for heated solutions, which caused propyhtization of the neighbouring rock, and 
introduced pyrite contaminated to a greater or less extent with other metals. The walls 
of the fissures were more impregnated with sulphides than the bulk of the propyhtized rock. 
Perhaps, also, the fissures were filled with lode-material. 

(2.) Later descending meteoric solutions caused a reconcentration of the ore- 
material, disseminated through the country, in the fissures, and produced the existing 
ore-bodies. 

* Page 99. 



108 

This hypothesis postulates secondary enrichment of lean primary ore-deposits. 
The primary ore-deposits are essentially the whole mass of propyhtized rock, of which 
the walls of the fissures were especially rich. As to the source from which the materials 
of these primary deposits were derived the writer offers no suggestion, beheving 
that any discussion of this point involves so many elements of a purely speculative 
nature as to be unprofitable. 

/ There is another question upon which the Karangahake mining- area offers some 
evidence, and that is the depth beneath the drainage-level of a district to which 
descending meteoric waters may descend. In the Bonanza section of the Maria lode 
oxidized ore is replaced by sulphide ore between Nos. 11 and 12 levels, or about 100 ft. 
above sea-level. In the TaUsman section it extends to below No. 12 level, or, say, 
100 ft. below sea-level. In the Welcome lode oxidized ore is found nearly 400 ft. 
below sea-level. Again, in the Bonanza section descending waters, although no longer 
oxygenated, have deposited ore at a depth of nearly 400 ft. below . sea-level and 500 ft. 
below the oxidized portion of this section. It is thus seen that meteoric waters 
have descended at least 500 ft. below the present boundary of the vadose and deep- 
circulation water-systems, and that oxygenated waters have descended 500 ft. below 
the present drainage-level. The oscillations in level of the Hauraki Peninsula have 
already been discussed, and it was shown that the movement at present is, on the 
whole, upward. This movement was initiated after the extrusion of the younger 
rhyohtes of the Waihi Plain, and at Karangahake was at least 800 ft. Before the 
extrusion of the younger rhyolites there is reason to beheve that a great valley 
existed to the east of Waihi. The floor of this valley is now near sea-level, implying 
that the present surface is not as elevated as it was before the extrusion of the 
younger rhyolites. There does not seem to have been a sufficient elevation at that 
time, however, to raise the lowest portion of the oxygenated ore at Karangahake 
even to the level of the sea, and the evidence seems to indicate that the oxidation of 
the ore in the Crown Mines and the formation of the zoned sulphide ore of the Maria 
lode was brought about by meteoric waters which descended below the drainage-level 
of the district by several hundred feet, along fracture-zones. Van Hise* defines the 
belt of weathering as ending at the ground-water level, but the occurrence at Karanga- 
hake would indicate that oxidation may penetrate, under favourable conditions, some 
hundreds of feet below the level of the ground-water. Similar conditions obtain at 
Waihi and have been reported from mining-fields in other parts of the world. 

Future Prospects. 
Karangahake. 

If the theory of ore-formation advanced by the writer be accepted as a working 
hypothesis, the observed facts permit of conclusions more or less definite. Large 
accumulations of ore will not be found in the continuation of the dominant fissures 
north of the Waitawheta River into Taukani Hill, nor will ore be found in large 
quantities beyond the most southern hmits of the ore as now determined. These 
conclusions are reached from a consideration of the topography. The greater portion 
of the rich sulphide bonanza of the Tahsman Mine has already been opened up, and 
the diminution of value in depth will be relatively abrupt. This conclusion is based 
on the high percentage of zinc showing in the lower portions of the ore-body as now 
developed. Zinc in Schiirmann's table occupies a relatively low position. 

* Van Hise, C. R. : " Treatise on Metamorphiem," Monograph, U.S. G.S., xlvii, 1904, p. 163. 



109 

Te Aroha. 

Te Aroha mining area has recently suffered considerable elevation. As far as the 
weathering of the rocks are concerned, the area may be considered " juvenile." The 
ore-bodies have not yet reached the stage of maturity or of concentration obtaining 
at Karangahake. The sulphide-enrichment zone has not yet migrated to the foot of 
the mountain-slopes ; it 'is still to be found a considerable distance up the slopes. No 
ore has yet been found in the lodes where they cross the streams, nor will it ever be 
found there in any quantity. Discoveries of good ore may yet be made on the steep 
ridges and slopes of the mountain, but these are not Ukely to be more important 
than those already made. 

Waitakohe. 

The mass of propyhtized rock in this locahty is not great when compared with 
the Karangahake and Te Aroha mining -areas. Moreover, the area is topographically 
young, and concentration of the ore will yet proceed further. Such a process requires 
many thousands of years, and the maintenance throughout that period of conditions 
favourable to ore-deposition. 



no 



CHAPTER VIII. 





MINING CLAIMS. 




Talieraaii (.'onsolidated — 


Page. 


Crown Mines — continued. 


Page 


Area and Production 


.. 110 


Underground Workings 


115 


Maria Lode 


. . Ill 


Drainage 


115 


Other Lodes 


.. Ill 


Ore-tre^tnient 


115 


Faults . . 


.. 112 


Power 


116 


Underground Workings 


.. 112 


Costs 


IIH 


Drainage 


.. 112 


Dominion Gold-mining Company 


110 


Ore-treatmont 


.. 113 


Te Aroha Claims — 




Power 


. . 113 


Hardy's Mines 


110 


Costs 


.. 113 


Waitawheta Gold-prospecting Com- 




Grown Mines — 




pany 


117 


Area and Production 


.. 113 


Bendigo Gold-mining Company 


117 


Welcome Lode . . 


.. 114 


Seddon Gold-mining Company 


118 


Other Lodes 


.. 114 


Tui Mine 


118 


Faults 


.. 115 


Eliza Mine . . 


118 



Talisman Consolidated. 
Area and Production. 
This company, registered in London under the title of " The Talisman ConsoUdated 
(Limited)," holds in all an area of 507 acres 2 roods 36 perches, made up as follows : 

Adeline Reefs . . 
Adeline Reefs Extended 
Crown Extended 
Imperial 
TaHsman 

Talisman Extended 
Victor- Waihou . . 
Woodstock United 

507 2 36 
Other claims which at one time covered portions of the same ground are the Ivanhpe, 
Truro, Kenilworth, Hauraki, Bonanza, Golden Fleece, Dubbo, Diamond, Rose, &c. 
The output from the various claims to the end of 1911 is as follows : — 

Value. 



A. 


E. 


p. 


85 





29 


v.) 





26 


30 








62 





18 


60 








79 


2 


15 


99 


1 


10 


72 


1 


18 







Long Tons. 


Oz. . 


£ 


TaUsman . . 




. 426,993 


2,305,442 


1,425,293 


Woodstock* 




. 49,165 


139,767 


116,862 


Ivanhoef . . 




1,275 


1,165 


18,500 


Kenilworth 




121 


. , 


5,746 


Dubbo 




12 


54 


53 


Crown Woodstock . 




3 


4 


11 


Adeline 




347 


2,410 


5,582 


Diamond . . 




107 


573 


1,433 


Rose 




15 


63 


62 


Imperial 




16 


41 


103 






478,054 


2,449,519 


1,573,645 



* Absorbed in Talisman, 1904. 



t Absorbed in Woodstock, 1894. 



Ill 

No records fivi; available previous to the year 1887, and up to and includinji 1895 
the value of the bullion obtained is estimated only. 

Maria Lode. 

Of the many reefs which traverse the property only five have been exploited to any 
extent. These are the Maria, Woodstock, Shepherd's, AdeHne, and Imperial lodes, and 
of these the Maria has yielded all save a comparatively trivial amount of the bulUon 
won. 

The great Maria fissure has been traced for a length of nearly 100 chains. Its 
strike and dip have already been described. Five more or less distinct pay-shoots occur 
along its course ; these, from north to south, are the Ivanhoe, Woodstock, Talisman, 
Bonanza, and Dubbo shoots respectively. 

The Ivanhoe shoot lies in that portion of the fissure occurring in Taukani Hill. 
It has been worked by the Sir Walter Scott, Ivanhoe, and Truro companies, but the 
present holders have not exploited it. The ore of this shoot is oxidized, 3 ft. to 4 ft. 
in thickness, and has been worked to a depth of about 400 ft. from the crest of Taukani 
Hill. 

The Woodstock shoot lies immediately to the south of the Waitawheta Stream. 
The ore is oxidized, and varies from 2 ft. to 12 ft. in thickness. Several minor faults 
traverse the shoot, and are genetically related to it. 

The TaHsman shoot also carries' oxidized ore only. It has been worked for a 
vertical depth of 1,500 ft. Down to No. 13 level this shoot contained oxidized milling 
ore, but in No. 14 level the lode is small and irregular and the country is unoxidized. 
The southward-dipping Woodstock fault apparently runs out of this shoot at or just below 
No. 13 level. 

The Bonanza shoot was worked in the upper levels from No. 1 to No. 6 level. 
Here it carried oxidized ore. For the next 400 ft. the dip flattened, and the ore was 
lean and unpayable. In No. 8 level milUng ore again appeared in this shoot, and has 
continued to the lowest level yet opened, No. 14. Between No. 11 and No. 12 levels 
the oxidized ore gave place to sulphide ore. In general, oxidized ore in this mine 
contains four parts of silver to one of gold ; in No. 11 level the ore, though still 
oxidized, carried fifteen of silver to one of gold ; in No. 12, in sulphide ore, the pro- 
portion is about ten to one ; in No. 13 level, three to one ; in No. 14, one to one ; 
while in the intermediate, 80 ft. lower, the gold is more abundant than the silver. 
From No. 8 level downward each level lias so far shown an increase in the length 
of the payable ore, until in No. 14 level the length is over 1,100 ft., and the width 
about 4 ft., and sometimes up to 10 ft. Where the lode flattens in dip, as just below 
No. 11 level, and between Nos. 12 and 13, the ore is lean, and the width small. An 
east branch of the Maria lode appeared first m No. 10 level of the Bonanza section, 
and has been exploited down to No. 13 level. In No. 13 a western branch appears 
also. Map 7 shows the levels driven on these branches. 

The Dubbo shoot yielded milling ore in its upper portion above No. 2 level, Dubbo 
section. It was explored with unsatisfactory results in No. 4 level, and again in 
Nos. 10, 11, and 12 levels. In No. 13, however, sulphide ore of high value has been 
found, but sufiicient work has not yet been done to show the extent of miUing ore. 

Other Lodes. 

About 600 ft. west of the Woodstock section of the Maria lode the Woodstock lode 
occurs. This lode only carried milling ore close to the outcrop, where also the surround- 
ing rock was extensively siUcified, forming the " Woodstock Blow." 



112 

Shepherd's lode occurs less than 300 ft. to the west of the Woodstock section of 
the Maria lode. In the upper levels this lode was small, averaging, say, 30 in., but 
carried high-grade ore. At 350 ft. below the outcrop the ore became poor, and was 
not explored again until No. 12 level. A crosscut from this level proved the fissure 
to be filled with breccia, without any sign of lode material. 

The Adehne reefs occur about 25 chains to the eastward of the Maria lode. They 
were worked by the Adehne, Diamond, and Rose companies. Two lodes with a west- 
ward dip and a strike of about N. 20° E. (magnetic) were worked, the largest about 
12 in. in width. Very Httle can be learned concerning these lodes. 

The Imperial lode, worked by the United and Imperial companies, is probably 
a northern continuation of the Adehne. The lode varied between 2 ft. and 3 ft. in thick- 
ness, and strikes north-east. It continues into the bed of the Waitawheta Stream as 
a zone of sihcification. 

Faults. 

Numerous east-and-west striking faults traverse the property held by the TaHsman 
Consohdated, and dislocate the lode fissures. Usually the displacement of these faults 
is not great, from 5 ft. to 20 ft., but sometimes it may amount to 50 ft. Maps 7 and 8 
show the position and dip of some of the main faults. 

Underground Workings. 

To understand the underground workings, it must be borne in mind that until 
1904 the Woodstock and Ivanhoe sections of the mine belonged to a separate company, 
and that the Tahsman, Bonanza, and Dubbo shoots had perforce to be exploited 
independently of the rest of the Maria fissure. Thus, from No. 8 level in the Tahsman 
there is an inchne shaft, in part along the dip of the lode, to No. 14 level, and until 
the absorption of the Woodstock this shaft alone gave access to the deeper workings. 
At present the main entrance of the mine is by the Woodstock No. 5 or River level, 
which is 40 ft. below No. 11 level, Tahsman. About 100 ft. from the mouth of this 
adit a shaft (the Woodstock shaft) has been sunk vertically. This will ultimately 
be connected with the lowest workings, and will permit the men to reach the working- 
faces much more readily than by the present route via the ladderway of the Tahsman 
shaft. 

The ore from the passes is trucked to the Talisman shaft and tipped into hoppers, 
of about 70 tons capacity, beneath the levels ; thence it is hoisted in skips by. air- 
winch placed in No. 11 level to the top of the Tahsman shaft, at No. 8 level. From 
here it is trucked by horse-tram to bins at the upper terminal of an aerial tram, 
worked as a self-acting jig, which dehvers the ore directly to the battery storage-bins. 
A separate small hopper is provided at each level for waste rock, which is hoisted 
to the river adit only and trucked out to the mullock-tip. The Tahsman shaft has 
four compartments below No. 11 level — namely, two ore-skip ways, one waste-skipway, 
and one ladderway and pipe-compartment. Above this level the waste-skipway does 
not exist. Maps 7 and 8 show the distribution of the levels and winzes of the 
Tahsman Mine. 

Drainage. 

Surface-water is picked up as far as possible at No. 7 level, and no water in 
quantity is encountered until the deeper workings are reached. At present drainage 
below the River level is effected through the Tahsman shaft by two Hfts of air- 
driven pumps. At the time of the writer's visit a 24 in. Cornish set was in course 
of erection at the Woodstock shaft. Boilers to supply steam for this pump have 
been erected near the mouth of the Woodstock No. 5 level. 



Plate X. 



Waitawhetu Eiver. 




Kakanoahakk Mountain, showing Talisman Power-house and Mill in Foreground. 




Gio. Bull. No. 16.} 



Talisman i'o web-house, 



[To face qi. 11.3, 



113 

Ore-treatment. 
The rougli mine ore from the aerial-tramway bin, which holds about 220 tons, is 
broken in two stages by Blake-Marsden crushers, and is then elevated to a conveyor- 
belt, which distributes it to the feed-bins. The fifty stamps are mechanically fed, and 
crush about 3-94 tons per head in twenty-four hours through a 15-mesh screen. The 
pulp goes through three tube mills, and is then elevated to classifiers, which dehver 
the overflow to the amalgamating-tables, and return the coarse sand to the tube mills. 
There are ten copper plates, each 4 ft. 9 in. wide and 12 ft. long, with a fall of 1 1 in. 
per foot. From the plates the pulp goes to travelhng-belt vanners, which separate 
about 2 tons of concentrate per day. From these the tailing goes to the cyanide- 
vats, where the sand is leached. The strength of solution, time of treatment, &c., 
has to be varied to suit the different classes of ore coming from the mine. The 
overflow from the sand-vats is thickened by spitzkasten and in settHng-tanks, and 
the sUme thus produced is treated with cyanide-solution in tall air-agitation cylinders. 
The solution is extracted and the shme washed by means of vacuum-filter baskets of 
the fixed frame type. Precipitation is effected in the usual way. The concentrate from 
the vanners used to be shipped to smelters, . but is now treated at the mill by cyanidation. 

Poiver. 
Most of the power required in mine and mill is obtained from Babcock and 
Wilcox boilers fitted with chain-grate mechanical stokers, which work admirably with 
the Huntly brown coal. The Ohinemuri and Waitawheta rivers supply an amount of 
water-power, varpng according to the precipitation. 

Costs. 
For the year ending February, 1912, the total working-cost, including construction 
and equipment, was £2 3s. 4-3d. per ton, made up as follows : — 

£ a. d. 

Construction and equipment . . . . . . ..058-3 



Mine-development 
Mining 
Milling 
Karangahake office 



9 
12 
13 

2 



0-9 
1-3 



2 3 4-3 
There were 47,000 tons of ore crushed, for a yield of bulhon estimated to be worth 
£233,297 14s. lid. 

•Of the gold-contents, 93-6 per cent, were recovered ; and of the silver, 80-6 per 
cent. : an average recovery by value of 92'1 per cent. 



Crown Mines. 
Area and Production. 
The company owning this property is registered in London under the title of " The 
New Zealand Crown Mines Company." In all, an area of 404 acres and 15 perches 
is held, made up as follows : — 

Abbey 

Crown Mines 

Earl of Glasgow 

Mammoth 

Ravenswood 

Ravenswood Extended 





A. 


R. 


V. 




. 10 





25 




. 98 


31 




87 





11 




. 104 










. 90 










. 14 


2 


28 



8 — Ai-oha. 



404 15 



114 

The output to the end of 1911 is as follows : — 

Long Tons. Oz. ^^^^• 

Crown Mines .. .. .. 340,139 ■ 393,268 760,793 

Monastery .. .. .. 23 164 201 

Earl of Glasgow . . . . 246 389 938 



340,408 393,821 £761,932 

No records are available previous to the year 1887, and up to and including 1895 
the value of the bullion obtained is estimated only. 

At least nine lodes run through that portion of the property south of the Waita- 
wheta. Only the Welcome, Crown, Earl of Glasgow, Maria, and Eoderick Dhu lodes 
have been exploited, and of these the Welcome and Crown have yielded most of the 
bulUon won from this property. 

Welcome Lode. 

The Welcome lode has been traced for a length of over 60 chains. Its strike 
and dip have already been described. The lode is displaced by numerous faults, 
which divide the workings into blocks, but nothing in the nature of definite ore- 
shoots exist. North of the Waitawheta River is the Monastery section of the lode, 
where a strong reef still awaits exploration in the north face. The deepest workings 
on the Welcome lode are 320 ft. below sea-level. Here a small quantity of sulphide 
ore occurs, the rest of the ore throughout the lode, as far as developed, being 
oxidized. The fact that sulphide bonanza ores of very high grade occur in the 
Bonanza section of the Maria lode below oxidized ores renders any discussion of the 
possibihty of a similar bonanza existing in the Welcome fissure at a depth yet 
unattained a matter of commercial interest. Unfortunately, not enough is known of the 
factors controlUng the formation of bonanzas to allow a definite opinion being formed. 
The Maria and Welcome lodes both occupy strong fissures similar in strike and dip ; they 
traverse the same country, and are httle more than 1,000 ft. apart. On the other 
hand, the gold-silver ratio in the oxidized ore of the Maria is about one to four, while 
in the Welcome it is one to one. Again, sulphide ore appeared in the Maria lode 
about 100 ft. above sea-level, while oxidized ore occurs 300 ft. below sea-level in the 
Welcome. On the whole, the writer regards deeper exploration of the Welcome lode as 
a legitimate enterprise. 

Other Lodes. 

The Crown lode lies to the east of the Welcome lode. It dips at a high angle 
to the westward, while the Welcome dips at an angle of, say, 50° in the same direc- 
tion. The two lodes are very close together on No. 5a level of the mine, but here 
the country is very broken, and the lodes difficult to follow. Above No. 5a the lodes 
probably converge, but nothing definite is known. This lode has yielded a large ton- 
nage of ore from above the Waitawheta level, but has not been explored beneath this 
point. 

The Adehne lode hes about 400 ft. to the eastward of the Crown lode, but has 
not been exploited to any extent in this property. The Earl of Glasgow lode is pro- 
bably on the same fissure. 

The Maria lode enters the Crown Mines lease in two places — between the Talisman 
and Bonanza shoots, and again north of the Dubbo shoot. The westward dip of the 
lode carries it into the Tahsman ground near No. 6 level, Tahsman, in both localities. 
That portion of the Maria lode between the Tahsman and Bonanza shoots is now 
being attacked ; it is estimated to yield 23,000 tons of miUing ore. 



115 

FaiiUs. 
Numerous east-and-west striking faults traverse the property and dislocate the 
lodes. It has been found impossible to correlate these with the similar breaks occurring 
along the course of the Maria. In fact, all the faults belong to a great distributive 
fault, and are complementary to each other. Although the displacement of the lodes 
caused by any one of these faults is not great, they have proved a source of great 
trouble in mining, and add considerably to the development and mining costs. It is 
on account of the faults that the oxidation of the ore has reached so far below the 
water-level. 

Underground Workings. 

The main entrance is by the Waitawheta River level, by which both the Welcome 
and Crown lodes are exploited. The naming of the various levels proceeds from this 
level, the first level above being known as No. 1a and the first below as No. 1b. Above 
the Waitawheta level there is no regular shaft, connection being by winzes only. A 
large three-compartment underlay shaft has been sunk along the Welcome lode a few feet 
from the entrance of the main adit. The ore is dehvered to the mill with a minimum 
of handling, the trucks, which hold a ton, being run from the mine levels direct to the 
mill. 

Drainage. 

Surface-waters are not allowed to percolate below the Waitawheta level, and the 
lower workings are kept dry by a three-throw electrically driven pump fixed in the 
chamber of No. 5b level. The winzes sunk in the southern end of this level at present 
drain through to the Talisman workings. The water in the winze stands about 80 ft. 
above the lowest point drained in the TaHsman. 

Ore-lreaivient.* 

The ore in the mine-tnicks is taken in sets of ten to the battery, a mile from 
the mine, by horse traction. The trucks are raised one at a time up an inclined plane 
to the breaker floor. The ore is broken by a jaw crusher to pass a 2^ in. ring, and 
is fed to the stampers mechanically. 

A 0-4-per-cent. cyanide solution is used in the mortars, of which there are twelve 
in commission and foundations in position for four more. The stamps, which are from 
900 lb. to 1,000 lb. in weight, average 100 blows a minute. The screens used are 30 mesh, 
and 100 tons is crushed in sixteen hours, nearly 800 tons of solution being used in the 
operation. The pulp passes in part over amalgamating-plates and in part over blankets, 
and then goes to the 40-ton sand-vats, of which there are twelve. The sands are 
given a five-day treatment. The overflow from the sand-vats passes to the slime-vats, 
Ume being added from a berdan. The ore yields about 40 per cent, of slime. The 
overflow from the sUme-vats goes to storage-tanks, and is used in the battery. When 
a slime-vat is full it is allowed to settle, and then as much of the solution as possible 
is decanted, the remainder being drawn through the filter-bed by vacuum pump. The 
solution from the sand and slime vats is passed through zinc extractors, thence to 
concrete sumps to be again pumped to the battery feed-tank. The blanketings are 
treated by amalgamation in six berdans, and then passed into agitators, where they are 
cyanided. About 200 tons of solution are passed through the mortar-boxes during the 
night shift, to ensure a barren solution at the start of each day's crushing. 

The Crown Mines Company were the first to experiment with the cyanide treat- 
ment on a commercial scale, and in many ways their present treatment is out of date. 
It is proposed to install a modern vacuum-filter plant, and later tube mills also. 



* Prom notes by W. Gibson, School of Minos, Karangahake. 
8* — Aroha. 



116 

Po^ver. 
Water-power derived from the Waitawlieta River is used as well as steam-power. 

Costs. 
The costs per ton for the year ending 30th June, 1912, were as follows : — 
Mining and haulage — 



Mining . . 

Haulage 

Miscellaneous 
MilUng and treatment' — 

Reduction 

Treatment 

Miscellaneous 
Mine-development 



s. 

19-49 
0-60 
1-03 

3-89 
4-05 
1-30 
6-73 



Total cost per ton . . . . . . . . . . 37-09 

The bulUon -recovery for the same period was 90-43 per cent, of the value of the ore. 

Dominion GoLD-MiNiNfj Company. 

During the writer's stay at Karangahake this company was actively prospecting its 
holding. The lodes, of which several are known, occur in a western and an eastern group. 
The western lode or lode-group has been explored by several tunnels. Unfortunately, 
although the outcrops were promising enough^ the prospecting adits showed that the 
lode or lodes were fault-involved and very irregular. At present attention is directed 
to the numerous eastern lodes, and a low-level tunnel is being driven to test them in 
depth. At the time of the writer's last visit the face was in hard sUghtly propy- 
litized andesite. 

--.-.-. ■■■/ Te Aroha Claims. . 

Hardy's Mines. 
This company's claims contain numerous lodes, among which may be mentioned 
the Premier, Hero, Colonist, Welhngton, New Find, Galena, May Queen, Silver King, 
and Phcenix. These lodes have produced the following amounts : — 





Long Tons. 


Oz. 


Premier 


.. 11.505 


10,418 


Hero 


26 


13 


Colonist 


.. 9,248 


5,412 


New Find . . . . . . 


.. 28,889 


41,170 


Galena . . . . ... 


.. 800 


374 


May Queen ... 


218 


163 


Phoenix . . . . . . / 


. .. 27 


37 



50,713 57,587 

The Premier workings are on the Big Reef, where that zone of sihcification 
is joined by the Vulcan* lode. The shoot of ore was from 100 ft. to 250 ft., in lengthy 
and from 3 ft. to 8 ft. in thickness, and has been worked for a vertical height of 
about 240 ft. 

The Colonist shoot is also in the Big Reef, where it is joined by the Warrior 
lode. The shoot was about 130 ft. in length, and has been worked to a depth of 120 ft. 



* Formerly known as Golden Crown. 



117 

In the New Find section of the property two shoots have been worked, both 
being on the]|Big Reef, at the junction of cross-lodes. The northern shoot was about 
150 ft. in length and 16 ft. wide. It has been stoped for a distance of 300 ft. from 
the surface. There is about 300 ft. between the north and south shoots. The latter 
was 8 ft. wide and 130 ft. long. 

The Galena and May Queen are 3 ft. lodes, which carried a considerable amount 
of copper-pyrites and galena. 

The Welhngton is small, and yielded only oxidized ore. 

The Silver King lode has been exploited in this property at what are known 
as the Big Blow workings. About 4 ft. of the lode has been extracted for a 
length of 60 ft. and a depth of 20 ft. 

An adit 1,600 ft. in length was driven along the Big Reef from its southern 
end, and crosscuts across the lode at intervals proved the ore to be very low grade. 

At the time of the writer's visit a low-level tunnel was being driven to prospect 
the Colonist and Premier shoots in depth. The Hero reef was cut, and was found 
at this level to be 12 ft. in width, and to carry fair values for a length of 60 ft. 

This company owns a battery and cyanide plant, which are situated at Waiorpngomai . 
Township. The former is actuated by water-power. 

Waitawheta Gold-'prospecting Campany^ 

In the Westraha section of this company's holding the Vulcan lode, which here 
is from 4 ft. to 6 ft. in thickness, has been explored, and a small parcel broken for 
crushing. Arrangements were being made at the time of the writer's visit to transport 
the ore by the county tramway to Hardy's battery for treatment. 

lu the Loyalty- Welcome section the lodes have yielded the following amounts : — 

Long Tons. Oz. 

Welcome . . ' . . . . . . . . 2 113 

Loyalty . . . . . . .... 554 654 

Alexandra . . . . . . . . . . 14 96 

Inverness .. .. .. .. ..261 202 

831 1,065 

The Loyalty lode varies from 1 ft. to 5 ft. in thickness, and the bulUon it contains 
is associated with chalcopyrite. 

The Alexandra and Inverness are leaders from 2 in. to 1 ft. wide. 
Goldsworthy's lode, about 2 ft. thick, also traverses this company's ground. 

Bendigo Gold-mining Com.fany. 

The Silver King is the principal lode in this company's claim. This averages 
about 8 ft. where it has been worked. Besides this lode, the East -and- West, Werahiko, 
and Waitoki lodes have been exploited to some extent. The East-and-West lode is 
very large, and the Waitoki and Werahiko are each about 3 ft. in thickness. 

As far as can be ascertained, these lodes have yielded up to the end of 1911 as 
follows : - 

Silver King 

Werahiko 

Waitoki 

717 559 



Long Tons. 


Oz. 


. 180 


132 


. 414 


371 


. 123 . 


36 



118 

Tke company opened up the Silver King lode on the Trana level, and completed 
a low kvel beneath it, but here the lode was poor. They erected a small battery, 
driven by water-power, provided with rock-breaker, concentrators, and cyanide plant, 
and connected this plant to the county tram by aerial line. Unfortunately, the 
mine could not be made to pay. 

Seddon OoU-mimng Company. 

This company at the time of the writer's visit w&s driving a low level to cut the 
Seddon lode. 

Tui Mine. 

This claim is held by a syndicate. The name has often been changed, and is 
now Hercules ; nevertheless, it is better known as the Tui. The Champion lode runs 
through this property, and several parallel lodes also exist. There are five levels 
opening up the pipe of ore, which is narrow at the outcrop, and shortens at each 
level. From official sources 149 tons, valued at about £1,000, has been extracted, but 
this quantity is probably much too low. The ore is heavily mineralized with galena 
and zinc-blende, and also carries a little cinnabar. 

Eliza Mine. 

The Waitakohe Claim, better known as the Eliza, is situated on the steep northern 
Hank of the Waitakohe Valley. The lode, which may be traced for 20 chains, is 
about 4 ft. wide, has a strike of nearly 15° E. of N. (meridian) and a dip of 70° westward. 
The walls are well defined, and strongly pyritized. The fissure-filhng is in the main 
crushed country, with numerous small branching stringers of quartz and calcite traversing 
it. These stringers, which may be up to 2 in. thick, carry sulphides of silver, copper, 
lead, and zinc, as well as bullion. The lode has been explored by several drives, of 
which the lowest is the 600 ft. crosscut, which proved the existence also of a 4 ft. lode 
of calcite, as well as a parallel fault-system. 



liy 



CHAPTER IX. 



SUMMARY OF THE ECONOMIC POSSIBILITIES OF THE AROHA SUBDIVISION. 



Page 
Gold- silver Mining . . . . ..119 

Metalliferous Deposits other than Gold- 
silver Lodes . . . . . . 120 

Stone for Commercial Purposes . . 120 

Clays .. .. .. ..120 



Lignite . . . . . . . . 121 

Soils .. .. .. ..121 

Timber . . . . . . 122 

Kauri-gum . . . . . . . . 122 



Gold-silver Mining. 

This section is mainly a reiteration of what has been already said on preceding 
pages. The ore-bodies owe their formation to a secondary concentration, by descending- 
meteoric waters, of lean primary ore-bodies, which in the case of the Aroha Subdivision 
probably consist of masses of propylitized rock. Thus ore-bodies cannot exist in 
non-propylitized areas, nor in such areas beyond the reach of the descending waters. 
It follows, then, that the locahzation of ore-bodies depends, in the first place, upon the 
degree and extent of the area of propylitization, and, in the second place, upon the 
topography of the mining-area and the nature and extent of the circulation-channels 
followed by the meteoric waters. It must be confessed, however, that other factors, 
at present httle understood or perhaps altogether unknown, also have considerable 
influence, and render any conclusions as to the nature, extent, or position of ore-bodies, 
even in closely studied and relatively well-known localities, decidedly precarious. 

The Karangahake area is a region where intense propyUtization and marked 
topographical rehef obtain. The two principal lodes traversing it have yielded great 
quantities of bulhon. In the Welcome lode the bottom of the rich bonanza seems to 
have been reached, nor can it be expected that the rich sulphide ore of the Maria 
will attain depths much greater than those already explored. The other fissures of 
the district do not seem to have been such important circulation-channels as the 
two just mentioned, and what ore they carry is hkely to be confined to the higher 
horizons. Most of the ore from beneath Taukani Hill has probably been already 
won, while southward from the present workings, if one may judge from surface 
indications, the intensity of propyUtization rapidly diminishes. 

The topography of the Te Aroha area is even more marked than that obtaining 
at Karangahake, but the country is by no means so strongly propylitized, and the 
circulating solutions do not seem to have had sufficient time to produce the maximum 
amount of ore-concentration. Thus the ore-bodies hitherto found have neither been 
as extensive nor as rich as those of Karangahake, nor have they reached as great 
depths. It is the writer's opinion that further ore-bodies may be found at Te Aroha, 
but that they will not prove more profitable than those hitherto worked. There is 
one other matter in connection with the Te Aroha area which deserves mention, and 
this is its possible continuation down-faulted beneath the flats near Waiorongomai. 
That the country in which the lodes are enclosed is continued southward, down- 
faulted beneath the plain, is highly probable, and that portions of it are propyUtized 
there is no reason to doubt, but that ore-bodies exist is highly improbable. For the 
ore-bodies of Te Aroha are only now in course of formation, and secondary ore 
deposition is not hkely to occur under the conditions here present. 



1^0 

in the Waitakohe area propylitization is not' nearly so intense as at Karangahake 
or Te Aroha. Ore-bodies are likely to be small, and close to the present surface. 

Alluvial gold is found in the Whatakao Stream, but occurs neither in the Aonga- 
tete immediately to the north nor in the Wainui to the south. The Wairere also 
yields fine alluvial gold on careful panning. On the watershed between the Te Puna 
and Wairoa quartz sheading and alluvial gold may be obtained. Again, near Okauia. 
on the slope descended by the Tui Track, loose opahne quartz occurs. All these 
occurrences may be regarded as due to ancient small hot springs rising through the 
rhyolite tuffs. 

In the Waipupu Stream several boulders of propyhtized rock with small quartz- 
veins were observed, but could not be traced to an outcrop in situ. 

Auriferous reefs are said to occur at one other locahty within the Aroha Subdivision— 
in the slates outcropping in the south-west corner of the Waitoa Survey District. Fine 
alluvial gold was washed from every creek tried in this locality, but no reefs were 
observed. There is, however, no reason to doubt their existence, and they are pro- 
bably analogous to the lodes existing at Hunua on the western side of the Hauraki 
Gulf, and at Tokatea and Kuaotunu on the eastern side. It is possible that at one 
time an andesite cap covered the slates of this locality, and that the lodes once 
penetrated into this cap. The remnants which may exist are not likely to have any 
commercial value. 

Metalliferous Deposits other than CIold-silver Lodes. 

The mines of the subdivision have all yielded from time to time a small amount 
of the ores of copper, lead, and zinc, while mercury has also been found, but in ver}' 
sftiall quantity. The principal value of all the ores hes in their gold-silver content. 

Copper-ore is reported to have been found in the upper valley of the Wharawhara, 
and also in the Parengorengo, close to its debouchure on the plain. No areas of 
propyhtized rock were observed in these localities. 

Stone 3<^oe Commercial Purposes. 

The chief use to Avhich the vast deposits of hard rock within the subdivision is 
put is to macadamize roads. This method of road-formation might be more freely 
used, with great benefit to the farmer, on the plains of the Waihou and Piako. The 
quarry at Te Aroha which supplies the greatest quantity of broken rock is situated 
in a consoUdated breccia. The andesitic flows so abundant in this portion of the 
district would yield a better class of road-metal. 

At the present time no use is made of the building and ornamental stones which 
could be obtained in great variety from the flow and fragmental rocks of the subdivision. 
In this respect the breccias and tuffs are the more valuable, in that they are more 
regularly jointed than the flow rocks, 

Clays. 

The extensive deposits of clays suitable for brick and tile making, which form part 
of the Tauranga ■ Series, are a valuable asset to the district. Rough bricks of excellent 
quality have been made from these clays, and at the time of the writer's visit a small 
brickmaking plant was in course of erection on the banks of the Wainui. Some of the 
clay-beds which occur so abundantly in the Piako district should also be found useful 
for this purpose. At no distant date the rich swamp lands of the subdivision should 
become sufficiently valuable to make profitable the substitution of subsoil-tile drainage 
in place of the open ditches at present used. 



121 

Lignite. 

The thick seams of lignite occurring at various places around the southern 
portion of Tauranga Harbour should have consideralile value as sources of fuel when 
firewood becomes less plentiful. The lignite, before use, should be stored under cover 
to permit of the evaporation of some of the contained water. Mr. Earl, of Aongatete, 
assured the writer that when so treated the lignite was equal to the best manuka 
firewood for steam-raising purposes. 

This fuel should also be admirably adapted for burning in brick-kilns. Producer- 
gas plants should also be able to utiUze this fuel to advantage. In this connection 
the faciUty with which water transport to Tauranga could be effected must not be 
forgotten. 

The probabihty of coal-measures occurring beneath the Hauraki Plain has already 
been discussed (see p. 81). 

Soils. 

It is not proposed in this place to discuss the mode of formation of soils. Briefly, 
a soil consists of rock chemically and mechanically decomposed and mixed with a 
variable amount of matter of organic origin, known as humus. The fertihty of a 
soil is dependent upon several factors — its chemical composition, its physical state, its 
humus-content, the amount and regularity of the moisture-supply, and the temperature. 
Man can control to a greater or less degree all of these factors, and it is in theii- 
intelUgent adjustment that success in farming lies. Each soil to be !made economically 
most efficient requires special treatment. 

Soils may be either transported from a distance or derived from the decay of the 
underlying rocks. In an area which contains a complete range of rocks, from deposits 
of yesterday to mudstones -of Miocene age, this classification is unsatisfactory. The 
soils of the Aroha Subdivision will be considered as if residual from each rock-group. 

The small area of Trias- Jura rocks within the subdivision has a thin poor soil 
of httle value to the farmer or grazier. 

The rocks of the Andesite Series give rise to a very fair soil, but unfortunately, 
save in a few small areas, the rehef of the country of which they form the subsoil 
is so abrupt as to render it fit for grazing only. Fern, tea-tree, wineberry, &c., grow 
so readily in the genial chmate that it is a matter of difficulty to maintain permanent 
pasture on non-arable land. 

Similar remarks apply to the soils furnished by most of the members of the Dacite 
Series. The upper slopes of the Karangahake Mountain and the bare hills near Tirohia 
show examples of soil from the first and third member of the series respectively. 
The mudstones of the series, however, from their very nature, readily assume mature 
forms ; and in the valley of the Waitawheta, flats and low hills covered with soil 
derived from these beds afford excellent farm land. Small areas of arable land also 
occur in the valleys of the Waimata and Mangakiri. 

A considerable area of flat or gently undulating land within the subdivision has a sub- 
soil formed of the rocks of the Rhyolite Series. Notable examples of such areas are 
the so-called Waihi Plain and the higher portions of the Katikati Lowlands. The soils 
of both these areas are usually considered very poor. On the other hand, the soil of 
the Whakamarama Plateau, the underlying rock of which cannot be distinguished from, 
and grades into that of the Katikati Lowlands, is considered to be of excellent quahty. 
The difference in fertihty of the two soils is beheved to be chiefly due to the difference 
in humus-content. This is a question, however, which has been discussed in another 
place. 



12^ 

'i'tie sons yielded by the rocks of the Tauranga Series are among the best in the 
subdivision, and every available acre is under cultivation. 

The Recent Deposits furnish soils which are naturally of widely var3ang quality. 
The swamps, which until European occupation covered very large areas of the Piako 
Beds, when drained and the soil aerated afford first-class land, rich in humus, and 
admirably adapted for aU crops which grow well in a rather light soil. At present 
most of this land is used for dairying. 

The flood-plains of the larger streams afford small areas of rich land, which, how- 
ever, varies rapidly from heavy to light. 

The sand-dunes of the subdivision are mostly fixed, and used for the depasturage 
of sheep and cattle. 

In the south-east corner of the Tauranga Survey District superficial pumice-deposits 
cover an unknown area. As is well known, cattle and sheep depastured upon lands 
the subsoil of which is formed of recent pumice-deposits develop a form of anaemia 
known as " bush sickness " or " Tauranga disease." It has lately been definitely 
determined that this disorder is caused by a deficiency of iron in the soil.* Rhyolitic 
rocks, as a whole, contain httle iron ; but it should be noted that the disease does not 
occur, and affected animals actually recover, on lands with a subsoil formed of the 
older rhyohtic rocks of the subdivision. 

Timber. 
By far the most valuable timber yielded by the forests of the Aroha Subdivision 
is the kauri, the supphes of which are now rapidly approaching exhaustion. Less 
abundant and less valuable are the red, black, and white pine, totara, mangeao, and 
puriri. Even when the milUng-trees have been removed from the forests the remainder is 
of value either as mining-timber or as fuel. 

Kauri-gum. 

Kauri-gum, to an amount of which even an approximate estimate cannot be given, 

has been derived chiefly from the fern-covered slopes of Hikurangi Mountain and of 

the hiUs eastward of Waihi. Gum-digging is stiU practised in a desultory way, but, 

as far as this subdivision is concerned, is never likely to provide more than a most 

precarious hvelihood. 

* Aston, B. 0. : " The Chemistry of Biish Sickness." Journal of the Department of Agriculture, vol. v 
1912, pp. 121-125. 



V2'6 



INDEX. 



A. 



Acknowledgments, 1 . 

Agriuultural industries, 1 8. 

Allen, F. B., 8, 90. 

Alluvial gold, ftl, 120. 

Alunite, 90. 

Amalgam, natural, 91 . 

Ananui Waterfall, 24. 

Andesite from Karangahake described, Ol . 

Andesite from near Owharoa described, ttl . 

Andesite from Waihi Plain described, 74. 

Andesite Series — 

Age and correlation of, B.T. 

Distribution of, ^S. 
Andesites, 56. 

Hornblende, 58. 

Petrology of, 59. 

Pyroxene, 58. 

Succession of, 59. 
Andesitic accumulations, extent and nature of, 81. 
Andesitio obsidian from Waihi Plain described, 61 . 
Andesitic rocks, analyses of, 62. 
Anglesite, 92. 
Ankerite, 90. 
Antimony, 92. 
Aongatete Stream, 23. 
Area of Aroha Subdivision, 1 . 
Argentite, 91 . 

ArgiUite in breccia. Talisman Mine, 55. 
ArgiUite reported in Woodstock Mine, 55. 
ArgiUites in situ, 57. 
Arsenic, 92. 

Ariariparitapu Mountain, 20. 
Aroha Subdivision — 

Area of , 1 . 

Structure of, 52. 
Ascension theory of ore-genesis, 102. 
Azurite, 92. 



B. 

Bartrum, J. A., 1. 

Bastite, 59. 

Bell, J. M., 8, 9. 

Bell, J. M., and Fraser, 0., 9, 63, 68, 70, 78. 81, 94, 

98, 102, 103, 104. 
Bendigo Gold-mining Company, 15, 117. 
Bonanza Shoot, Talisman Consolidated, 111. 
Bornite, 92. 
Bramhall, H., 6. 
Bromargyrite, 91. 
BuUion-production, 13, 15, 110, 114, 116, 117. 



C. 
Cadell, H. M., 7. 
Calcite, 90. 
Calcite as ganguo, 94. 
Calcite lode-fUling, analyses of, 105. 
Californian quail, 4. 
Callipepla californica, 4. 
Campbell, J., 7. 

Thermohyperphorio process of, 15. 
Cape Colville earth-block, 53, 55. 
Cape Colville Range, 20. 

Structure of, 53. 



Cashmore Bros., 19. 

Cerussite, 92. 

Chalcopyrite, 92. 

Cheal, P. E., 22. 

Chinese pheasant, 4. 

Cinnabar, 91 , 96. 

Clarke, F. W., 40. 

Clays, 120. 

Climate, 2. 

Coal, Dickey Flat, 58. 

Coal, Tarariki Creek, Waihi-Tairua Subdivision, 

59. 
Coastal plain earth-block, 54. 
Coast-line, 24. 
Cobalt, 90. 

Colonial Exploration Company, 14. 
Contract System, 17. 
Copper-ores, 120. 
Country — 

Influence of nature of, 98. 

Karangahake, analyses of, 106. 
CovelUte, 92, 94. 

Cox, S. H., 5, 6, 50, 57, 58, 63, 67, 68, 76, 88, 91 . 
Crawford, J. C, 5. 
Crocoite, 92. 
Crown Mines — 

Area and production of, 113. 

Costs of, 116. 

Drainage of, 115. 

Faults of, 116. 

Lodes of, 114. 

Ore, treatment of, 115. 

Power of, 116. 

Underground workings of, 115. 
Crystal tufEs, dacitic, 64. 
Cussen, L., 7, 77. 

D. 

Daoite — 

Definitiou of term, 56. 

Karangahake-Mangakino Track described, 65. 
Daoite Series — 

Age and correlation of, 67. 

Distribution of, 63. 

Petrology of, 65. 
Daoites, succession of, 64. 
Dacitic rocks, analyses of, 67. 
Dairying industry, 1 8. 
Davis, W. M., 46. 
Davis, W. M., quoted, 50. 
Dead country, 99. 
Dean Creek, 64. 
Deforestation, 26, 27. 
Diefienbaoh, E., 4, 5. 
DiefEenbaoh, E., quoted, 49. 
Dioptase, 92. 

Dominion Grold-mining Company, 116. 
Don, J. R., 7. 

Don, J. R., quoted, 100, 106. 
Drainage of swamps, 28, 29. 
Driving logs, 19,27. 

Drowned valleys of Tauranga Harbour, 25. 
Dubbo shoot, Talisman Consolidated, 111. 
Dyke Series — 

Age and correlation of, 75. 

Analyses of rooks of, 75. 

Distribution of, 73. 

Petrology <>•' 74. 



124 



B. 



East Coast Road, 11. 
Electrum, 91. 
Eliza Mine, 1 1 8. 
Enstatite, 59. 
Epsomite, 90. 



P. 

Fault-complex — 

Bay of Plenty, 51 . 

Miranda, 51 . 

Thames, 49. 
Faults — 

Age of, 51 , 52. 

Clay bank, Kaiangahake, 84. 

Influence of, on ore-deposition, 97. 

Karangahake, 48. 

Mangapukatea-Kauritutahi, 48. 

Minden, 47. 

Okauia, 49. 

Parengorengo, 48. 

Puketutu, 48. 

Rahu Saddle, 48. 

Romani, 49, 84, 85. 

Te Rere-atu-kahia, 49. 

Thompson Track, 47. 

Waiharakeke-Waitakohe, 48. 

Waiorongomai, 49. 

Waipupu, 47. 

Waitoki-Orima, 49, 84. 

Wharawhara, 47. 
Fauna of Aroha Subdivision, 3. 
Financial conditions, 1 7. 
Finlayson, A. M., 9. 
Finlayson, A. M., quoted, 86. 
Fishing industry, 19. 
Flora of Aroha Subdivision, 3. 
Eraser, C, 9, 50, 55, 77, 81, 93, 98, 102. 
Eraser, C, and Adams, .T. H., 9, 63, 78, 81 , 98, 102. 
Frog, native, 4. 
Fumaroles, 93. 
Furnaces, smelting, 12, 14. 
Future prospects — 

Karangahake, 108, 119. 

Te Aroha, 109. 

Waitakohe, 109. 



G. 

Galena, 92. 
Galvin, P., 6. 
Gangue, 94. 
Grenesis of ore, 102. 

Ascension theory of, 102. 

Conclusion, 107. 

Lateral secretion theory of, 104. 

Secondary enrichment theory of, 102. 
Geological history, 82. 
Geology — 

Economic, 84-109. 

General, 55-83. 
Godwit, 4. 
Gold, 91. 

Gold-silver mining, possibOities of, 119. 
Gordon, H. A., 6, 8, 78. 
Gordon, H. A., quoted, 14. 
Orfiben, Hauraki, 8, 50. 81, 83. 
Graham, K. M., 2. 
Grauwacke, 57. 
Grauwaoke province, 52. 
Gregory, J. W., 40. 



H. 

HsBUsler, R., 6,91. 

Halloysite, analysis of, 90. 

Hangawera earth-block, 52, 55, 57. 

Hangawera Hills, 20, 81 . 

Hardy, E. H., 15. 

Hardy's Mines, 116. 

Hares, 4. 

Harker, A., 78, 80, 81. 

Harker, A., quoted, 57. 

Hauraki petrographical province, 78. 

Hauraki Plain, 20. 

Heaphy, C, 5. 

Hector, J., 5, 6, 7. 

Hessite, 91 . 

Hobbs, W. H., quoted, 46. 

Holland, P., quoted, 73. 

Hone Werahiko, 13. 

Howell, John, 14. . 

Hunga Hunga Swamp, 24, 28. 

Hunter, Ashley, 6. 

Hutton, F. W., 5, 6, 58, 77. 

Hyalite, 90. 



I. 



Iddings, J. P., quoted, 57. 
Industries, 12. 
Influence of man, 26. 
Influence on ore-deposition of — 

Faults, 97. 

Nature of country, 98. 

Topography, 97. 
lodargyrite, 91. 
Island shelf, 24, 54. 
Ivanhoe shoot, Talisman Consolidated, 111. 



J. 



Jarman, A., 9, 95. 
Jarman, A., quoted, 17. 
Jura-Trias Formation, 57. 



K. 

Kaimai Road, 1 1 . 

KaoHnite, 90. 

Karangahake, history of mining at, 12. 

Karangahake mining-area — 

Analyses of rocks from, 106. 

BuUion-produotion of, 13. 

Dip of lodes in, 85. 

Faulting of, 84. 

Future prospects of, 108, 119. 

Lode fissures of, 85. 

Physiography of, 84. 
Karangahake Mountain, structure of, 84. 
Katikati — 

Lowlands, 21 . 

Mineral springs, 39. 

Old Track, 1 1 . 
Katipo,4. 

Kauri, distribution of, 3. 
Kauri-gum, 3, 122. 
Kauri Timber Company, 1,18. 
Kauritutahi Stream, 23, 47. 
Kerargyrite, 91. 

Keripehi bore, composition of water from, 38. 
Kindly country, 99. 
Kirk, C.T., 87. 
Kiwi, 4. 
Kopurererua Stream, 23. 



125 



L. 

Labour conditions, 17. 

La Monte furnace, 12. 

Larnach, W. J. M., 6. 

Lateral secretion theory of ore-genesis, 103. 

Lava-flows, proportion of breccias to, 56, 58. 

Levat, D.,8. 

Lignite — 

Matakana Island, 76. 

Omokoroa Point, 76, 121 . 

Tauranga Beds, origin of, 76. 

Wainiata Creek, 65, 68. 

Whatakao Stream, 76. 
Linionite, 92. 
Liopelma hochstelteri, 4. 
Lindgren, Waldemar, 5, 8, 22, 50, 70. 
Literature, 5. 

Lode-filling, analyses of, 105. 
Lode minerals, 89-92. 

Lodes, distribution of metallic contents of, 94. 
Lodes, persistence in depth of, 93. 
Lodes — 

Adeline, 112. 

Alexandra, 117. 

Arizona, 98. 

Champion, 98, 11 8. 

Colonist, 98, 116. 

Crown, 85, 94, 97. 

Diamond Gully, 98. 

Dominion, 85. 

Earl of Glasgow, 114. 

East-and-West, 98, 117. 

Eureka, 98. 

Galena, 98, 116, 117. 

Goldsworthy's, 117. 

Hero, 98, 116, 117. 

Imperial, 112. 

Inverness, 98, 117. 

Islington, 98. 

Loyalty, 98, 117. 

Maria, 85, 94, 95, 97, 111. . 

May Queen, 98, 116, 117. 

Mikado, 98. .:.. 

Moa, 91, 98. 

Montezuma, 98. 

New Find, 13, 98, 116, 117. 

Palace, 98. 

Phoenix, 98, 116. 

Premier, 94, 96, 116. 

Roderich Dhu, 114. 

Seddon, 98. 

Shepherd's, 93, 112. 

Silver King, 98, 116, 117, 118. 

Sir Walter Scott, 85. 

Tui, 14, 96, 98. 

Vulcan, 98. 

Waiorongomai Buck Reef, 88, 93, 97, 116. 

Waitoki, 117. 

Warrior, 98. 

Welcome, Karangahake, 95, 97, 114. 

Welcome, Te Aroha, 98. 

WeUington, 98, 116, 117. 

Werahiko, 98, 117. 
Loughnan, R. A., 8. 



M. 

Maokaytown, rhyolites near, 68. 
Maclaren, J. M., 9, 50. 
Maclaurin, J. S., 2, 30. 
Magnetic pyrites, 92. 
Mangakino Stream, 49, 89. 

Daoites of, 64. 
Mangapukfttea Stream,' 23, 48. 



Mangroves, 3. 
Maori population — 

In 1841, 10. 

In 1859, 10. 
Maoris, distribution within Aroha Subdivision, 10. 
Marcasite, 92. 
Marshall, P., 8, 58. 
Matakana Island, 24, 25, 26. 

Dunes of, 28. 

Raised beaches of, 75. 

Rocks of, 58, 77. 
Maukoro, raised beach at, 77. 
Maunganui Mountain, 24, 26, 53, 68. 

Raised beach at, 77. 
Maungawhio-tapu Hill, rocks of, 64, 65. 
McCombie, J., 2, 7, 13. 
McCombie, J., quoted, 12. 
McKay, A., 7, 8, 63, 67, 68, 70, 77, 78. 
Meanders of Waihou, 21, 24. 
Means of communication, 10. 
Melanterite, 90. 
Mercury, 91. 
Mesozoic Formation, 55. 

Micropoecilitic structure in andesites, cause of, 60. 
Minden Peak, 68, 69. 
Mineral springs — 

Katikati group of, 39. 

Okauia group of, 36. 

Origin of, 39^5. 

Te Aroha group of, 30. 

Waitoa group of, 37. 
Mine-waters, analyses and nature of, 99, 100. 
Mining and treatment of ores, 16. 
Mining claims, 110. 
Mining industry, history of, 12, 
Mirabilite, 90. 
Montgomery, A., 6. 

Morgan, P. G., 8, 9, 50, 68, 69, 70, 71, 72, 91. 
MorrinsviUe-Miranda Road, 11. , 
Mottled country, 98. 
Motuhoa, 26. 
Motuopui, 26. 
Motu Otau, 25, 26, 68. 
Moturiki, 26. 
Mountains, 20. 

Mud-banks and sand-bars, Tauranga Harbour, 78. 
Mudstone series, distribution of, 64, 65. 



N. 

Nevadite, 66. 

Ngatamahinertia Mountain, 20, 54. 
Ngatukituki Mountain, 20. 
Nickel, 90. 



0. 



Ohinemuri River, history of, 21, 22, 82, 84. 

Okauia mineral springs, 36, 37. 

Okohukura Spring, 36. 

Omokoroa Point, 25, 76. 

Opal, 90. 

Opawe Swamp, 28. 

Ore, analyses of, 95. 

Ore-genesis — 

Ascension theory of, 102. 

Conclusion, 107. 

Lateral secretion theory of, 104. 

Secondary enrichment theory of, 103. 
Origin of mineral springs, 39-45. 
Orima Creek, 49, 84. 
Owharoa — 

History of mining at. Hi. 

Mining-area, 89. 

Tramway, 18. 



126 



Pan-amalgamation plants, 12, 14. 

Panipani, 24, 25, 26. 

Parengorengo Creek, 23, 48. 

Parkes's furnace, 12. 

Park, J., 4, 6, 7, 8, 9, 22. 50, 55, 58, HI, 68, 70, 73, 

81, 82, 88, 92, 94. 
Paruparu Spring, 36. 
Patarere Plateau, 53, 54. 
Pateroa Range, 20. 
Persistence of lodes in depth, 93. 
Petrographical province, 57, 78. 
Phasianus torquatus, 4. 
Physico-chemical data, 100. 
Physiography, general features of, 20. 
Piako — 

Beds, 77. 

River, 21. 

Swamp, 24, 28. 

Swamp waters, composition of, 41. 
Platinum, 91. 

Pohomihi Stream, " wilsonite " in, 68. 
Pond, J. A., 6, 32, 90, 92. 
Population, Aroha Sulsdivision, 10. 
Poupou Stream, 23. 
Propylitization, cause of, 60. 

Characteristics of, 86. 

Period of, 81. 

In relation to lodes, 92. 
Pukeko, 4. 

Puketutu Stream, dacitic rocks of, 64. 
Pumice-deposits, superficial, 78. 
Pyrargyrite, 92. 
Pyrite, 91 . 



Quail, Californian, 4. 
Quartz, 89. 



R. 



Rabbits, 4. 

Radial movements, 80, 81. 

Railey's pan-amalgamation plant, 12. 

Railways, 11. 

Rainfall, 2. 

Raised beaches, 77. 

Ramaroa Spring, 36, 41. 

Recent Deposits, 77. 

Rere-atu-kahia. (See Te Rere-atu-kahia.) 

Rhodochrosite, 90. 

Rhyolites, 56. 

RhyoKtes and Post-rhyolitic dykes, correlation of, 

82. 
Rhyolite Series, distribution of, 68. 
Rhyolite tuff, "wilsonite," description of, 70. 
Rhyolite, Waihi, description of, 72. 
Rhyolitic rocks, age and correlation of, 73. 

Analyses of, 69, 73. 

Petrology of older, 69. 

Petrology of younger, 70, 71, 72. 

Succession of, 68. 
Rift VaUey, 52. 

Initiation of, 82. 
River gravels and swamp deposits, 78. 
Rivers, 21. 
Roads, 11. 

Ruangarara Stream, 54, 69. 
Rutley, F., 7, 8, 69, 70. 
Rutley, P., quoted, 72. 



s. 



Sand-dunes, 27, 78. 

Schiff, F., 7. 

Schurman's table, 96. 

Secondary enrichment theory of ore-genesis, 103. 

Seddon Gold-mining Companj', 118. 

Sheehan Bros., spring on farm of, 37. 

Shotover basin, alluvial gold of, 91 . 

Silting of rivers, 28, 29. 

Silver, native, 91 . 

Skey, W., 6, 90, 91. 

Smith, S. P., 5. 

Soils, 121. 

SoUas, W. J., 8, 65, 69, 70, 72, 86. 

SoUas, W. J., quoted, 60, 61, 62. 70, 71, 74. 

Sphalerite, 92. 

Springs dependent on surface-waters, 20. 

Stansfield, H., 2, 95. 

Stokers, mechanical, 1 13. 

Stone for commercial purposes, 120. 

Stoping methods, 16. 

Streams, age of, 23, 24, 50. 

Structure of Aroha Subdivision. 52. 

Suess, E., 40. 

Swamps, 24. 



T. 

Talisman Consolidated — 

Area and production of, 110. 

Costs of, 113. 

Drainage of, 112. 

Faults of, 112. 

Lodes of, 111. 

Ore-treatment of, 113. 

Power of, 113. 

Underground workings of, 112. 
Talisman, ore-analyses of, 95. 
Talus deposits, 78. 
Tamaki Creek, 22. 
Taukani HiU, 84, 119. 
Tauranga and Walton Beds, 75. 

Age and correlation of, 76. 
Tauranga Beds, 75. 

Former extent of, 76. 

Lignite of, 76. 

Origin of, 82. 

Succession of, 76. 
Tauranga Harbour, 11, 19, 25. 

Drowned valleys of, 25. 

Mud-banks of, 78. 

Swamps round, 24. 
Tauranga, population of, 10. 
Te Aroha — 

Monthly temperature at, 2. 

Mountain, 20, 88. 

Population of, 10. 
Te Aroha mineral springs — 

Gas-content of, 31 . 

Origin of, 40, 41. 

Radio-activity of, 30. 

Table of composition of, 32-35, 42. 

Therapeutic value of, 31. 
Te Aroha mining-area — 

Bullion production of, 15. 

Future prospects of, 109, 119. 

History of, 13. 

Lode fissures of, 88. 

Physiography of, 88. 
Te Ho, 24, 26, 54, 68. 
Te Hopai Island, 26. 
Te Karewa Island, 4, 25, 54, 68. 
Te Kopukairoa Mountain, 68. 



1^7 



Temperature, luouthly, 2. 

Te Puke Road, 11. 

Te Puna Springs, 39. 

Te Puna Stream, 54. 

Te Rere-atu-kahia Spring, 39. 

Te Rere-atu-kahia Stream, 23, 49. 

Te Weraiti Mountain, 20. 

Thames River, 21 . 

Thompson's Track, 1 1 . 

Tidal erosion, 25. 

Tidal range, 25. 

Timber industry, 18, 122. 

Topography, influence on ore-geuesis, 97. 

Tracks of subdivision, 1 1 . 

Tramways of subdivision, 11. 

Trias- Jura Formation, 57. 

Tribute mining, 17. 

Tuahu Track, 11, 55. 

Tuapiro Spring, 39. 

Tuapiro Stream, 22, 23. 

Tuatara, 4. 

Tuff from Ravenswood described, 62. 

Tui Mine, 14, 118. 

Tui Track, 11. 



Valeucianite, 60, 90. 

Van Hise, 0. R., 108. 

Van't Hoff, J. H., 100. 

Views of other geologists, 4, 57. 

Viticulture, 18. 

Volcanic eruptions, cause of, 80. 

Volcanic rooks, table of analyses, 79. 

Von Hochstetter, F., 4, 5, 67, 77, 88. 

Von Hochstetter, F., quoted, 50. 



w. 

Wad, 90. 

Waiau Stream, 22, 23, 47. 

Waiharakeke Stream, 23, 48. 

Walhi Plain, 21,22. 

Waihi, rainfall at, 3. 

Waihi Sawmilling Company, 1, li 

Waihoii River, 21 . 

Silting of, 28. 
Waimapu Stream, 23. 
Waimata Stream, 22. 

Lignites of, 65. 
Wainui Stream, 23, 54. 



Waiorong()mai County Tram, 14. 
Waiorongomai Stream, 23, 49. 

" Wilsonite " in, 68. 
Waipapa Stream, 23, 54. 
Waipupu Stream, 23, 47, 120. 
Wairakau Stream, 23. 
Wairere Fall, 23. 
Wairere Stream, 23, 54. 

Alluvial gold of, 120. 
Wairoa River, 23. 
Wairoa Stream, 22, 47. 
Waitakohe mining-area, 89. 

Future prospects of, 109, 120. 

History of, 16. 
Waitakohe Stream, 23, 48. 
Waitanui Stream, 22. 
Waitawheta earth- block, 53. 
Waitawheta Gold -prospecting Company, 117. 
Waitawheta River, 22. 
Waiteariki FaU, 23. 
Waiteariki Spring, 37. 
Waiteariki Stream, 23, 54. 
Waitekauri Stream, 22. 
Waitoa River, 21. 
Waitoa springs, 37, 38. 
Walton Beds, 75, 76. 
Walton springs, 38. 
Waterfalls, 23. 

Water-power, 23, 24, 113, 116. . 
Wauchope, J. A., 7. 
Weathering, 87. 
Weed, W. D., 102. 
Weka, 4. 

Wells, R. G., quoted, 96. 
Whakamarama earth- block, 53. 
Whakamarama Plateau, 20, 23, 28, 53. 

Rocks of, 64. 

Timber of, 3, 19. 
Whanga. (See Whakamarama.) 
Wliarawhara Stream, 23, 47. 
Whatakao Stream, 23, 26, 54. 

Alluvial gold of, 120. 
" Wilsonite " — 

Description of, 70. 

Nature of, 71 . 
Wilson, W. R., 7, 14. 
Wind-breaks, necessity of, 28. 
Winds, Aroha Subdivision, 2. 
Wine-making, 18. 
Wohlmann, A. S., 9. 
Wohlmann, A. S., quoted, 31. 
Woodstock Blow, Talisman Consolidated, HI. 
Woodstock Shoot, Talisman Consolidated, 111. 



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